Competition Law and Market Boundary Erosion

1. Introduction

Market boundary erosion refers to the gradual weakening of traditional boundaries between markets because of technological convergence, digital platforms, multi-sided ecosystems, vertical integration, interoperability, data accumulation, bundling, network effects, and changing consumer behaviour.

Traditional competition law often begins by asking:

What is the relevant product and geographic market?

Market boundary erosion complicates this question because products that were previously separate can increasingly constrain one another. A smartphone may function as a payment device, advertising platform, shopping gateway, entertainment device and financial-services interface. Likewise, cloud computing can connect with software, artificial intelligence, cybersecurity, data storage and enterprise applications.

The legal problem is therefore two-sided:

1. Overly narrow boundaries may exaggerate market power by ignoring emerging substitutes.
2. Overly broad boundaries may conceal market power by treating weak or indirect competitors as effective constraints.

Modern competition analysis increasingly examines competitive relationships across adjacent markets and ecosystems, rather than assuming that historical industry classifications remain stable.

2. Meaning of Market Boundary Erosion

Market boundaries traditionally depend upon:

• product substitutability;
• geographic substitutability;
• consumer preferences;
• price and quality;
• cross-elasticity of demand;
• supply-side substitutability;
• entry conditions.

Boundary erosion occurs when these distinctions become less stable.

Example

Suppose there were historically three separate markets:

Banking → Payments → Digital Wallets

A technology platform subsequently offers:

Messaging + wallet + payments + lending + shopping + advertising.

The competitive constraints can no longer be understood entirely by examining each historical market separately.

Thus:

Traditional market

Product A ↔ Product B

may become:

Product A ↔ Platform ↔ Product B ↔ Product C ↔ Product D

The platform can therefore exercise influence beyond the conventional boundaries of any single product market.

3. Major Causes of Market Boundary Erosion

A. Technological convergence

Technological developments can cause formerly distinct products to become substitutes.

Examples include:

• smartphones and cameras;
• streaming and television broadcasting;
• cloud computing and traditional IT infrastructure;
• digital wallets and banking services;
• online marketplaces and conventional retail;
• AI assistants and traditional search;
• connected vehicles and mobility services.

Competition authorities therefore need to examine functional substitutability, not simply product labels.

B. Platform ecosystems

Platforms frequently connect several markets.

For example:

Operating system → App store → Payment system → Advertising → Cloud → AI services

A firm may have substantial influence over the ecosystem even where its share in one individual product market appears relatively modest.

The EU's contemporary approach expressly recognizes that digital ecosystems can contain several interlinked products and services whose markets may be horizontally or vertically connected.

C. Multi-sided markets

A platform may simultaneously serve:

• consumers;
• advertisers;
• merchants;
• developers;
• suppliers;
• content providers.

Consequently, a market cannot always be analysed solely from the perspective of one customer group.

Competition on one side may influence competitive conditions on another side.

D. Data-driven competition

Data can blur market boundaries because the same dataset may support multiple products.

For example:

Search data → advertising → AI training → recommendation services → e-commerce

A company may therefore use an advantage developed in one market to strengthen its position in another.

E. Bundling and tying

Bundling can effectively extend a firm's competitive position from one market into another.

The relevant question becomes:

Is the second product genuinely independent, or has the firm's control over the first product altered the competitive conditions in the neighbouring market?

This issue was central to several technology antitrust cases.

4. Traditional Legal Framework

A. Relevant product market

The relevant product market generally includes products that consumers regard as sufficiently substitutable.

The classic principle is associated with United States v. Brown Shoe Co.

The inquiry considers:

• reasonable interchangeability;
• cross-elasticity of demand;
• characteristics of products;
• intended use;
• pricing;
• industry structure.

The important lesson is that market boundaries are analytical constructs, not merely industry classifications.

B. Hypothetical monopolist / SSNIP analysis

The hypothetical monopolist test asks whether a hypothetical monopolist could profitably impose a small but significant and non-transitory increase in price.

But digital markets create difficulties because:

• services may be free;
• competition may occur through quality;
• privacy may be an important competitive parameter;
• innovation may be difficult to quantify;
• switching costs may be substantial;
• network effects may matter more than price.

Consequently, competition authorities increasingly consider non-price competition.

5. Six Important Case Laws

1. United States v. Brown Shoe Co., 370 U.S. 294 (1962)

Facts

Brown Shoe and Kinney were involved in the manufacture and distribution of footwear. The proposed combination raised questions about the appropriate boundaries of the relevant footwear markets.

Principle

The Supreme Court recognized that a broad industry can contain economically significant submarkets.

The Court considered factors such as:

• industry or public recognition;
• product characteristics;
• distinct customers;
• specialized vendors;
• specialized facilities;
• distinct prices;
• sensitivity to price changes.

Relevance to market boundary erosion

Brown Shoe establishes an important methodological point:

Competition law does not have to accept the industry's broadest possible definition of a market.

At the same time, market boundaries cannot be constructed artificially merely to produce a particular competitive result.

2. United States v. E.I. du Pont de Nemours & Co. — Cellophane, 351 U.S. 377 (1956)

Facts

The case concerned DuPont's position in cellophane and competing flexible packaging materials.

Principle

The Supreme Court examined reasonable interchangeability and cross-elasticity of demand.

The case became particularly important for the proposition that products outside a narrow product category may constrain the defendant if consumers readily substitute between them.

Relevance

Cellophane illustrates the opposite side of market-boundary analysis:

If boundaries are drawn too narrowly, existing substitutes may be improperly excluded.

It also demonstrates the danger of the Cellophane fallacy: observing substitution at an already elevated monopoly price may make the relevant market appear artificially broad.

Thus, market boundary erosion must be analysed carefully rather than simply assuming that observed substitution proves effective competitive constraint.

3. FTC v. Staples, Inc., 970 F. Supp. 1066 (D.D.C. 1997)

Facts

The FTC challenged the proposed Staples–Office Depot merger.

The parties argued over whether the relevant market should encompass the broader sale of office supplies or the narrower market for consumable office supplies sold through office superstores.

Decision

The court accepted the narrower market.

It found evidence that Staples and Office Depot treated one another as particularly important competitive constraints, while other retailers did not exert the same degree of competitive pressure.

Relevance

Staples demonstrates that:

The existence of numerous sellers in a broad industry does not necessarily mean that all sellers impose equivalent competitive constraints.

This is crucial when analysing market-boundary erosion because the emergence of superficially similar products does not automatically destroy a relevant market boundary.

4. United States v. Microsoft Corp., 253 F.3d 34 (D.C. Cir. 2001)

Facts

Microsoft's conduct concerning the Windows operating system and web browsers was examined under U.S. antitrust law.

Importance

The case is particularly significant for platform markets and technological convergence.

Microsoft's operating-system position provided a strategic platform from which it could influence adjacent software markets.

The court examined issues including:

• browser competition;
• operating-system barriers to entry;
• network effects;
• exclusionary conduct;
• platform control.

Relevance to boundary erosion

Microsoft demonstrates that competition may occur between layers of a technological ecosystem.

The relevant competitive question is not necessarily:

"Are browsers and operating systems the same product?"

Rather:

"Does control over one technological layer enable a firm to influence competition in an adjacent layer?"

This concept has become increasingly important in modern platform regulation.

5. Google Android — Google and Alphabet v. European Commission, Case T-604/18 (General Court, 2022)

Facts

The European Commission examined Google's Android ecosystem and various restrictions involving:

• Google Search;
• Android;
• mobile application distribution;
• Google Play;
• browser applications.

The General Court's judgment discussed the interconnected nature of Google's products and the ecosystem surrounding Android.

The EU's contemporary market-definition framework specifically refers to the Android judgment when describing a digital ecosystem as involving several categories of users and interlinked products.

Relevance

The case illustrates how competition analysis can move beyond isolated products.

The ecosystem can involve:

Operating system → App distribution → Search → Browser → Advertising

Consequently, competitive conditions in one layer can affect competition in another.

6. Google Shopping — European Commission Decision AT.39740 (2017)

Facts

The European Commission investigated Google's conduct concerning comparison-shopping services.

Google was found to have given favourable positioning to its own comparison-shopping service within its general search results.

Competition issue

The case concerned the relationship between:

• general search;
• comparison-shopping services;
• online merchants;
• advertising and traffic acquisition.

Relevance to market boundary erosion

Google Shopping demonstrates that a platform operating in one market can become an important gateway to adjacent markets.

The competition concern therefore cannot always be understood solely by asking who competes directly with the platform's individual service.

The Commission's decision is also expressly referenced in the EU's modern ecosystem analysis.

7. Facebook/WhatsApp Merger — European Commission, Case M.7217 (2014)

Facts

Facebook's acquisition of WhatsApp raised questions concerning the relationship between:

• social networking;
• consumer communications;
• online advertising;
• data;
• mobile applications.

Relevance

The transaction illustrated an important feature of digital competition:

A transaction can have competitive significance even where the merging products do not simply overlap as conventional substitutes.

Data, network effects, user bases and future product development can create connections between adjacent markets.

This is particularly important in markets where the competitive value of users and data extends beyond the immediate service for which users are acquired.

8. Microsoft/Activision Blizzard

The Microsoft/Activision transaction provides a more recent illustration of the difficulty of applying conventional market boundaries to digital ecosystems.

Relevant competitive relationships included:

• gaming consoles;
• video games;
• cloud gaming;
• game distribution;
• subscriptions;
• operating systems and devices.

The case demonstrates the tension between analysing individual product markets and assessing competition between broader ecosystems. Contemporary academic analysis of the EU and UK decisions identifies precisely this tension between traditional market definition and ecosystem-level competitive assessment.

9. Booking/eTraveli

The Booking/eTraveli merger also illustrates the difficulty of analysing competition where businesses operate across interconnected digital services.

The transaction involved:

• online accommodation booking;
• flight booking;
• travel platforms;
• traffic acquisition;
• ecosystem effects.

The case is significant because it illustrates how a transaction can raise concerns concerning the competitive relationship between interconnected services even where conventional market definitions may appear relatively narrow.

10. Comparative Case-Law Matrix

11. Forms of Market Boundary Erosion

11.1 Horizontal boundary erosion

Occurs where products increasingly become substitutes.

Example:

Television
↓
Streaming
↓
Short-form video
↓
Social-media video

Competition may increasingly occur across historically separate categories.

11.2 Vertical boundary erosion

Occurs where a company expands across successive stages of a supply chain.

Example:

Cloud infrastructure → cloud platform → AI models → AI applications

Control at one level may affect competition at another.

11.3 Platform boundary erosion

A platform expands into adjacent services.

Example:

Search → Shopping → Payments → Advertising → AI

The firm's competitive position can therefore extend beyond the originally defined market.

11.4 Geographic boundary erosion

Digital commerce can reduce the significance of geographical boundaries.

For some markets:

Local market → national market → international platform

However, geographic boundaries may remain significant where there are:

• transportation costs;
• regulation;
• language barriers;
• local network effects;
• licensing requirements;
• physical infrastructure constraints.

The Staples litigation, for example, accepted metropolitan areas as relevant geographic markets because consumers' practical alternatives were geographically constrained.

12. Market Boundary Erosion and Digital Ecosystems

The modern ecosystem model can be represented as:

                 CORE PLATFORM                       │        ┌──────────────┼──────────────┐        ↓              ↓              ↓   Service A       Service B       Service C        │              │              │        └───────┬──────┴──────┬──────┘                ↓             ↓             DATA         NETWORK EFFECTS                │             │                └──────┬──────┘                       ↓                 USER LOCK-IN                       ↓             ADJACENT MARKET ENTRY

This creates a potential feedback loop:

Scale → data → better service → more users → stronger network effects → greater ecosystem power → expansion into adjacent markets

The European Commission has expressly incorporated the concept of digital ecosystems into its contemporary market-definition analysis.

13. Competition Risks Created by Boundary Erosion

A. Leveraging

A firm with market power in Market A may use that position to strengthen itself in Market B.

B. Self-preferencing

A platform may favour its own downstream service over independent competitors.

Google Shopping provides an important example.

C. Tying

Control over a core product can be used to encourage or require adoption of an adjacent product.

D. Bundling

Multiple products may be offered together, making it harder for independent competitors to compete with individual components.

E. Data leveraging

Data acquired in one market can potentially improve products or services in another.

F. Network-effect reinforcement

Expansion into neighbouring markets may increase the attractiveness of the firm's original platform, creating a self-reinforcing competitive advantage.

G. Foreclosure

A vertically integrated ecosystem can potentially restrict rivals' access to:

• users;
• data;
• APIs;
• distribution;
• payment systems;
• technical interfaces;
• advertising inventory;
• infrastructure.

14. How Competition Authorities Should Analyse Boundary Erosion

A structured framework can be used.

Step 1 — Identify the historical market

Determine how the market was traditionally defined.

Step 2 — Identify emerging substitutes

Examine technological and commercial developments.

Step 3 — Examine demand-side substitution

Ask:

Would consumers switch if the price, quality or conditions changed?

For digital services, examine quality, privacy, functionality and switching costs, not merely price.

Step 4 — Examine supply-side substitution

Can existing firms rapidly redirect capacity toward the product?

Step 5 — Identify adjacent markets

Map:

• upstream markets;
• downstream markets;
• complementary products;
• distribution channels;
• infrastructure;
• data markets.

Step 6 — Map ecosystem relationships

Identify whether one firm controls several interconnected layers.

Step 7 — Analyse network effects

Determine whether additional users increase the value of the service.

Step 8 — Analyse switching costs

Consider:

• data portability;
• interoperability;
• contractual restrictions;
• technical compatibility;
• learning costs;
• ecosystem investments.

Step 9 — Analyse conduct

Examine:

• tying;
• bundling;
• exclusivity;
• self-preferencing;
• discriminatory access;
• interoperability restrictions;
• refusal to supply;
• data restrictions.

Step 10 — Consider dynamic competition

The final question should not simply be:

"Who competes today?"

It should also consider:

"Who could realistically compete as technology and market boundaries evolve?"

15. Market Boundary Erosion and Merger Control

Market boundary erosion is particularly important in merger analysis.

A traditional merger analysis may ask:

Market A + Market A

But digital ecosystems can create concerns resembling:

Market A + complementary Market B + potential future Market C

For example:

Target  ↓ Users  ↓ Data  ↓ Adjacent service  ↓ Network effects  ↓ Higher ecosystem concentration

This means authorities may examine potential competition, ecosystem effects and dynamic competitive constraints, rather than merely calculating current market shares.

The EU's designation of major digital platforms as gatekeepers under the DMA also reflects the increasing regulatory importance of interconnected platform services.

16. Market Boundary Erosion and Market Power

Market boundary erosion does not automatically mean increased market power.

There are two possible outcomes.

Scenario A — Boundary expansion weakens market power

Traditional competitors        ↓ New technological substitutes        ↓ More competitive constraints        ↓ Reduced market power

Scenario B — Ecosystem expansion strengthens market power

Core platform      ↓ Adjacent markets      ↓ Data + network effects      ↓ Lock-in      ↓ Greater ecosystem power

Therefore, competition authorities must determine which effect is actually occurring.

17. Important Economic Indicators

Authorities may consider:

Structural indicators

• market shares;
• concentration;
• HHI;
• entry barriers;
• vertical integration.

Behavioural indicators

• switching rates;
• customer retention;
• multi-homing;
• pricing;
• bundling;
• exclusivity.

Digital indicators

• active users;
• network effects;
• interoperability;
• API access;
• data advantages;
• switching costs;
• ecosystem penetration.

Dynamic indicators

• innovation;
• potential entrants;
• technological convergence;
• R&D;
• disruptive technologies.

18. Legal Challenges

1. Static market definitions

Traditional market definitions can become obsolete rapidly in technologically dynamic industries.

2. Zero-price products

Where users pay no monetary price, SSNIP analysis becomes difficult.

3. Quality competition

Competition may concern:

• privacy;
• security;
• speed;
• accuracy;
• functionality.

4. Multi-homing

Users may simultaneously use several platforms, reducing or increasing the significance of market boundaries depending on the circumstances.

5. Potential competition

A firm outside the current market may nevertheless represent a significant future competitive constraint.

6. Ecosystem complexity

A single firm may simultaneously occupy multiple interconnected markets.

19. Key Doctrinal Principle

The central principle can be expressed as:

Competition law should define markets according to actual competitive constraints rather than historical industry labels.

But the opposite principle is equally important:

Competition authorities should not expand a market merely because products are technologically related.

There must be evidence of meaningful competitive interaction.

This balance is visible across the case law:

Brown Shoe → meaningful submarkets can exist.

Cellophane → genuine substitutes can expand the market.

Staples → apparently similar sellers may not exert equivalent competitive constraints.

Microsoft → platform control can affect adjacent technological markets.

Google Android → interconnected products may form an ecosystem.

Google Shopping → a gateway platform can affect downstream competition.

20. Conclusion

Market boundary erosion is one of the central challenges of modern competition law. Traditional competition analysis assumes reasonably identifiable product and geographic markets. Technological convergence, platforms, data, network effects, interoperability and ecosystem integration increasingly make those boundaries fluid.

The appropriate legal response is not to abandon market definition, but to make it more economically and technologically sensitive.

A comprehensive analysis should therefore combine:

Traditional market definition

• substitutability analysis
• non-price competition
• platform economics
• network effects
• data analysis
• ecosystem mapping
• dynamic competition
• potential competition