The Five Major Theories of International Law: History, Efficacy, Role & Practical Application

by. • • 2 min read
0
The Five Major Theories of International Law: History, Efficacy, Role & Practical Application "Comprehensive research post for law students & practitioners: the five theories of international law (Natural Law, Legal Positivism, Realism, Institutionalism, Critical Legal Theory), with history, cases (2023-2025), efficacy, step-by-step how to apply in litigation & policy, clickable footnotes & full references." "theories international law, natural law, legal positivism, realism, institutionalism, critical legal theory, how to apply, ICJ, WTO, jurisprudence"

The Five Major Theories of International Law: History, Efficacy, Role & Practical Application

Updated: 22 September 2025 • Author: Victor Okafor (Victor Strange) • For Law Students & Practitioners
Excerpt: Understanding the major theoretical paradigms of international law is essential not only for academic insight but for strategic litigation, treaty drafting, policy design, and assessing the likely success of claims. This article explains Natural Law, Legal Positivism, Realism, Institutionalism (Liberalism), and Critical Legal Theory, with recent case studies, deep analysis, and detailed step-by-step guides (“how to”) for using each theory in practice.
Contents:
  1. Introduction — Why Theory Matters
  2. Natural Law Theory
  3. Legal Positivism
  4. Realism
  5. Liberalism / Institutionalism
  6. Critical Legal Theory
  7. Comparative Efficacy & Combined Strategy
  8. Recent Cases (2023-2025) and Lessons
  9. Step-by-Step Application Template
  10. Clickable Footnotes & Bibliography

1. Introduction — Why Theory Matters

When law students or practitioners ask, “How do I build a strong argument from international law?”, “How likely is enforcement?”, “Which courts/institutions to use?”, theory provides the framework. Theories guide how we interpret treaties/custom, how we anticipate state behaviour, and how we design policy or litigation strategies. Without theoretical awareness, one risks using arguments that look good on paper but fail in practice.

Sources consulted include “Critical Examination of International Law Theories” by Adama Aloysious Gross (PAJES, 2024), recent EJIL articles on theory trends, ICJ & WTO case documents from 2023-2025, and leading scholarship on positivism, natural law, realism, institutional design, and critical legal theory. 0

2. Natural Law Theory

2.1 History & Origins

Natural Law traces back to ancient philosophers: Aristotle’s notion of universal justice, Stoics’ notion of a law of nature, Roman jurists’ ius naturale, medieval thinkers like Thomas Aquinas. In international law, natural law influenced early notions of jus gentium, law of war, humanitarian norms, and later the development of universal human rights in the 20th century. The idea that there are moral truths that law must reflect remains foundational in debates over justice, rights, and non-derogable norms.

2.2 Role, Importance & Efficacy

  • Role: natural law provides moral anchor: it justifies arguments for universal human dignity, foundational rights, responsibilities beyond positive law.
  • Importance: essential when treaties are silent/ambiguous, when positive law is abused, or in arguing for jus cogens norms and obligations erga omnes.
  • Efficacy: natural law becomes effective when its moral claims are adopted by states, reflected in treaties, customary law, court decisions; weaker where moral consensus is lacking or cultural disagreement is strong.

2.3 Recent Scholarship & Critique

Gross (2024) in PAJES surveys natural vs positivist theory showing that while natural law remains important in rhetoric (especially human rights, environment), its legal efficacy depends heavily on how many states treat the principle as binding, not just aspirational. 1

2.4 How-to: Applying Natural Law in Practice

  1. Identify a moral claim or principle (e.g. prohibition of genocide, preventing environmental harm) that your issue implicates.
  2. Search for evidence of adoption: international declarations, treaties, UN General Assembly resolutions showing moral consensus.
  3. Check if the principle is recognized as jus cogens or obligation erga omnes in court decisions or treaties.
  4. In litigation/advocacy, use the moral principle to fill gaps, but anchor your argument with positive law (custom, treaty) to show binding force.
  5. Anticipate counter-arguments: cultural relativism, state sovereignty, claims that the principle is not universally accepted or that moral claims exceed legal power.

2.5 Example Cases

ICJ Advisory Opinion: Obligations of States in Respect of Climate Change (2025) — moral ideas like intergenerational equity, human dignity, and environmental protection are emphasized. Though advisory, they influence treaty interpretation and domestic litigation. 2

Nuremberg Trials (1945-46) — early enforcement of natural law principles (crimes against humanity, war crimes) even before full codification. Serves as historical precedent for moral claims becoming legal obligations.

3. Legal Positivism

3.1 Definition & Origins

Legal Positivism argues that law is what is posited (created) by legitimate authority: treaties, agreements, customary law, judicial decisions. State consent is central. Not concerned with morality per se, except insofar as morality is incorporated via treaties or custom. Thinkers: Austin, Bentham, Kelsen, Hart. Kelsen’s “Pure Theory of Law” especially emphasises norms and validity apart from moral evaluation. 3

3.2 Role, Importance & Efficacy

  • Clarity and structure: positivism gives tools for determining what is binding.
  • Legal certainty: for treaty negotiators, states, litigators — you know what you are signing or what customary rules seem to bind states.
  • Efficacy: strong where treaty obligations are clear, where there is monitoring or dispute settlement; weaker when reservations, ambiguous custom, or lack of forums.

3.3 Recent Scholarship & Trends

The “Recent Trends in the Theory of International Law” (EJIL, 2026) article explores how positivist theory is still dominant in judicial decisions, especially those of ICJ, WTO, arbitral tribunals, but is increasingly challenged by normative claims (environment, human rights). 4

3.4 How-to: Applying Positivism in Practice

  1. Locate the treaty, convention, or custom relevant: confirm which states are parties, when treaty entered into force, the exact text.
  2. Check for reservations, declarations, ratification history — those change what a state has accepted or rejected.
  3. For customary law: assemble evidence of consistent state practice + opinio juris (statements, national law, voting records).
  4. Use interpretative tools like Vienna Convention Article 31–33 (treaty interpretation) if treaty applicable. 5
  5. In submissions or briefs, clearly show binding nature, avoid overreliance on moral claims unless you can show they are embedded in positive law.

3.5 Example Cases

ICJ Jurisdiction decision in Sudan v. UAE (2025) — the Court declined jurisdiction in part because of treaty reservation under Genocide Convention. Demonstrates positivist mechanics: treaty text + reservation matter more than moral claims alone. 6

Mali drone case v. Algeria (2025) — ICJ will not proceed until Algeria accepts jurisdiction; without clear consent, positivist norm holds. 7

4. Realism

4.1 Definition & Origins

Realism (in IR theory and legal theory) views international law as shaped by power. States comply when doing so aligns with their interests; when enforcement costs are low or political interest strong. Origins in 20th-century realism, based on thinkers like Hans Morgenthau, and in legal realism (U.S.), but applied to IL by scholars examining how power influences compliance and treaty design. 8

4.2 Role, Importance & Efficacy

  • Role: realism offers tools for risk assessment, for anticipating enforcement gaps, jurisdiction refusals, or selective compliance.
  • Importance: crucial for practitioners advising clients or states: understanding when a legal victory may not deliver in practice due to political resistance or power imbalance.
  • Efficacy: realism explains many real failures of enforcement, non-compliance, treaty avoidance; but realism alone doesn’t offer remedies — needs to be combined with institutional or normative strategies.

4.3 Recent Scholarship & Examples

Gross (2024) notes realism’s enduring explanatory power in his study on international law theories: many states ratify treaties but then evade compliance when political cost is high. 9

The 2025 ICJ cases (Sudan v. UAE; Mali drone case) show realism: states making jurisdiction reservations, withholding consent, using political leverage to delay or block adjudication. 10

4.4 How-to: Incorporating Realism Into Your Strategy

  1. Map power relations: which states have more legal resources, diplomatic clout, influence over institutions.
  2. Assess political costs & benefits: what a state risks (reputation, sanctions, trade, domestic politics) if it does or doesn’t comply.
  3. Include realistic fallback strategies: alternative forums, media / NGO pressure, coalition building.
  4. Don’t assume legal binding equals enforcement — build in non-legal levers (diplomatic pressure, publicity, trade leverage) into your litigation or policy plan.

5. Liberalism / Institutionalism (Regime Theory)

5.1 Definition & Historical Development

Liberal / Institutionalist theory emphasizes that in the “anarchic” international system, states create regimes, treaties, institutions (WTO, UN human rights treaty bodies, environmental regimes) to coordinate behaviour, reduce transaction costs, create norms, monitoring and enforcement mechanisms. Historical roots include Kant’s ideas of cosmopolitan law, the League of Nations, UN formation. Over time, treaty regimes have become more complex, with detailed monitoring, reporting, dispute resolution. Gross (2024) shows institutions’ role under many theories. 11

5.2 Role, Importance & Efficacy

  • Role: designing cooperative frameworks, enabling multilateral enforcement, reducing uncertainty.
  • Importance: treaty bodies, institutional design often decide how well obligations are performed.
  • Efficacy: high when the institution has strong compliance incentives, authority, and transparency; weaker when institutions are toothless, underfunded, or captured by powerful states.

5.3 Recent Scholarship & Illustrative Examples

Recent literature (EJIL 2026, “Recent Trends …”) indicates institutionalism is still effective in trade law (WTO), environment (Paris Agreement), human rights (regional courts), because these fields have strong institutionalization. 12

Case: WTO DSU remains one of the most reliable institutional enforcement systems (though political pressure and delays exist). Also, ICJ advisory opinion on climate change reinforces institutional obligations and reporting expectations under treaties. 13

5.4 How-to: Using Institutional / Regime-Theory Strategies

  1. Select the best institution/regime for the legal matter (e.g., WTO panels for trade, ICJ for state disputes, treaty monitoring bodies for human rights or environment).
  2. Examine treaty/institution design: dispute settlement options, reporting obligations, monitoring, sanctions or incentives.
  3. Use precedents of institutional rulings or reports as persuasive authority.
  4. Where institutions are weak, strengthen claims by seeking coalition backing (other states, NGOs), push for transparency or reporting mechanisms.
  5. Build policy or treaty proposals with strong institutional mechanisms to ensure future compliance (e.g. specifying timeline, review, sanctions or remedies).

6. Critical Legal Theory (Including Critical International Legal Theory, Post-colonial, Feminist & CLS)

6.1 Definition & Origins

Critical Legal Theory (CLT), Critical International Legal Theory (CILT), Critical Legal Studies (CLS), feminist legal theory, post-colonial critiques challenge formal legal doctrine, question whose interests law serves, expose power, bias, and inequality in legal systems. It argues that international law is not neutral or universal by default, but shaped by colonial history, political economy, gender, race, etc. Key thinkers: Martti Koskenniemi, Fleur Johns, Anthony Carty, scholars in EJIL and other theory journals. 14

6.2 Role, Importance & Efficacy

  • Role: revealing hidden assumptions, biases, power imbalances, colonial legacies, and pushing for legal reform, equity, and legitimacy.
  • Importance: gives voice to marginalized states, non-state actors; improves democratic legitimacy and fairness of international law.
  • Efficacy: often slower, less formal; influences law through scholarship, NGO advocacy, courts adopting critiques (interpretation), treaty drafting reforms; little direct enforcement but strong in shaping normative change and legal consciousness.

6.3 Recent Scholarship & Trends

EJIL’s “Recent Trends in the Theory of International Law” (2026) highlights how critical theories are increasingly intersecting with climate justice, indigenous rights, gender issues, digital sovereignty, and questioning universalism. 15

Gross (2024) also describes how functional and fictional theories are discussed alongside CLS; CILT is increasingly relevant in international legal education and in analyzing treaty practice especially in Global South. 16

6.4 How-to: Employ Critical Legal Theory in Practice

  1. Identify the power relations or inequalities in your issue: which states or actors are dominant, which are marginalized.
  2. Gather historical context: colonial history, treaty drafting history, power in negotiations, outside influences (economic, political) that shaped treaty text or custom.
  3. Use legal argument plus narrative / critique: show how legal texts or practices may marginalize or disadvantage certain actors; use case law or treaty practice that recognizes such critiques.
  4. Push for interpretive approaches in domestic or international courts that consider fairness, equity, contextualization (e.g., taking account of poverty, development, social rights) rather than only formal equality.
  5. Where possible, advocate for treaty reform, inclusion of minority/gender perspectives, transparency in treaty negotiations, or reparative justice (e.g. acknowledging colonial legacies, land restitution, climate debt).

7. Comparative Efficacy & Combined Strategies

No one theory works in isolation. The strongest arguments and strategies often combine them. For instance:

  • Use legal positivism to establish what binding law exists; use natural law or critical theory to argue for stronger moral obligations or fill normative gaps.
  • Realism helps anticipate non-compliance or obstruction; institutionalism helps build mechanisms to increase compliance.
  • Critical legal theory can help you frame issues of bias, fairness, legitimacy — useful in persuasive briefs, domestic courts, treaty reform, even if not decisive in strict adjudication.

This comparative strategy is especially effective in Global South litigation, climate justice, indigenous rights, human rights, where power imbalance, colonial history, weak institutions often diminish pure positivist or institutionalist claims unless supplemented by moral/normative and critical lenses.

8. Recent Cases (2023-2025) and Lessons for Practitioners

  • Mali Drone Case — ICJ, September 2025: ICJ declared that Mali’s lawsuit against Algeria cannot proceed unless Algeria accepts jurisdiction. This illustrates positivism (jurisdiction & consent) and realism (power to withhold jurisdiction) in action. 17
  • ICJ Advisory Opinion on Climate Change (2025): Reinforcement of natural law & institutional obligations: even advisory opinions carry normative weight, influence treaty interpretation and domestic and international legal culture. 18
  • Sudan v. UAE — Genocide Convention Jurisdiction (2025): Demonstrates how treaty reservations block jurisdiction; positivist theory central, realism helps predict resistance. (Press reports & ICJ registry) 19
  • WTO DSU recent disputes: Various trade panels in 2024-25 show that states comply better when the panel's rulings are paired with trade consequences and institutional oversight. (Examples: US-China trade, environmental exceptions) — institutionalism + positivism yield efficacy. [Note: specific case names omitted for brevity]
  • Critical theory influence in human rights and climate litigation: Increasing domestic court decisions in Global South referencing colonial history, equity, climate justice, rights of future generations. Gross (2024) notes treaties and courts in Africa and Asia citing equity and fairness rather than only formal treaty text. 20

9. Step-by-Step Application Template: How to Build a Strong Argument

Use this template in research, litigation, treaty drafting or policy advocacy to combine theory & practice:

  1. Define the Issue Precisely: identify subject matter (e.g. human rights abuse, environmental harm, trade dispute), parties involved, legal obligations in question.
  2. Select Legal Sources / Norms: treaty text, customary law, general principles — apply positivist theory for binding law; identify moral/normative claims if treaty/custom silent or disputed.
  3. Assess Jurisdiction & Consent: check if court/institution has jurisdiction, whether states have accepted it, if reservations exist.
  4. Map Political / Power Landscape: assess which states have power to avoid compliance, what political costs are, what diplomatic, economic leverage exists.
  5. Use Institutional Mechanisms: monitoring, reporting, dispute settlement — choose institution that gives remedy, transparency and enforcement (or at least visibility).
  6. Use Normative / Critical Lens: bring in fairness, equity, historical injustice if relevant; show bias or exclusion in treaty negotiation or practice; use moral arguments where legal ones are weak but normative claims are gaining acceptance.
  7. Prepare for Implementation or Enforcement: consider domestic incorporation, capacity, public opinion, NGO pressure, media attention, coalition building.
  8. Anticipate Counterarguments & Weaknesses: treaty silence/reservations, lack of cooperation, institutional weakness, jurisdiction limits, non-binding norms.

10. Clickable Footnotes & References

  1. “Legal Positivism,” Oxford Public International Law, entry. 21
  2. “Recent Trends in the Theory of International Law,” EJIL (2026). 22
  3. Reuters — Mali Drone Case (ICJ, 2025). 23
  4. The Guardian — Caribbean reaction to ICJ climate advisory opinion (2025). 24
  5. Gross, Adama Aloysious, “Critical Examination of International Law Theories,” PAJES, Vol. 5 No. 2 (2024). 25
  6. “Legal Realism,” OUPIL entry. 26
  7. “Sovereign Equality / Principles of International Law,” OPIL entry. 27
  8. Fleur Johns, “Critical International Legal Theory,” SSRN / Cambridge etc. 28
  9. Mali Drone Case re-reported. 29
Selected Bibliography & Further Reading:
  • Gross, Adama Aloysious. “Critical Examination of International Law Theories,” Pan-African Journal of Education and Social Sciences (PAJES), Vol. 5 No. 2 (2024). 30
  • “Recent Trends in the Theory of International Law,” *European Journal of International Law* (EJIL), 2026. 31
  • “Legal Positivism,” Oxford Public International Law (OPIL) entry. 32
  • “Legal Realism,” OPIL entry. 33
  • Johns, Fleur E., “Critical International Legal Theory,” SSRN / Cambridge Chapter. 34
  • Reports & press releases of ICJ: Mali Drone Case (2025), Sudan v. UAE (Genocide jurisdiction), ICJ Advisory Opinion on Climate Change. 35
  • Kelsen, Hans. *Pure Theory of Law*. (on validity, normativity, separation of law and morality). 36
4.94 / 169 rates

Post a Comment

Previous Post Next Post