The United States’ “swift” troop withdrawal from Afghanistan, the U.S.’ longest war spanning four different U.S. presidential administrations, is a subject of fierce debate in many legal and non-legal circles.

Although there appears to be no neutral position when discussing this issue, an approach based on a public international law principles provides an interesting dimension to the ongoing discussion.

International Law on Ending a War Between States

Any discussion on the law of troop withdrawal also necessitates a discussion on the law of ending a war when such war is fought between nation-states. However, the end of the conflict in Afghanistan presents an interesting addition to this discussion, given the sudden apparent change in leadership in Afghanistan as U.S. troops withdrew.

Formal Means of Ending a War

International law dictates that a war fought between two nation-states can end either through formal means or informal means.

With regard to formal means, the classical and ideal method for ending an interstate war is the conclusion of a formal peace treaty between the states. Traditionally, peace treaties have had a significant impact on the evolution of international law, from the treaty of Westphalia in 1648 to the Versailles treaty in 1919.

In fact, the series of peace treaties signed at the close of World War I contained, in their first part (Articles 1 to 26), the Covenant of the League of Nations, predecessor of the United Nations.¹

Despite their unique political standing, peace treaties are no different juridically from other types of interstate agreements, and are considered valid under Article 52 of the 1969 Vienna Convention on the Law of Treaties if they are not imposed on the defeated party by the victorious party through duress.²

Alternatively, war can be terminated under formal means by an armistice agreement. Under traditional international law, an armistice agreement was viewed as a pause in the fighting, similar to a truce or a cease fire.

However, modern understanding of armistice agreement, which arguably traces its origins in the armistice agreements that ended World War I, prescribes that armistice agreement means a termination of hostilities, completely divesting the parties of the right to renew military operations under any circumstances whatsoever.³

Essentially, it puts an end to the war. It does not merely suspend the combat.

Informal Means of Ending a War

Informal means for how a war may be brought to its conclusion includes implied mutual consent, debellatio, and unilateral declaration.

When warring parties enter into a peace treaty or an armistice agreement, war is terminated by mutual consent expressed in the instrument. It is not necessary that the mutual consent to end a war be verbalized by the parties. Such consent can also be inferred by implication from the parties’ behavior. For example, a state of war may come to an end by mere termination of hostilities by both parties.

Similarly, war may also come to an end if one of the parties is defeated to the point of its total disintegration as a sovereign nation. In this case, since the war would no longer be considered interstate in character, it will terminated by itself.

Termination under this scenario is referred to as debellatio. Debellatio necessarily involves effective military occupation of the local territory by the occupying state, all organized resistance has disappeared, and the government of the occupied state no longer in effective control.^4​

And finally, just as war must begin with a unilateral declaration of war as prescribed in The Hague Convention (III), it can also end with a unilateral declaration to end the war. This process can be viewed not as an independent mode for bringing war to a close, but as an offshoot of one of the two preceding methods.

International Law on Troop Withdrawal

With regard to troop withdrawal, typically a party withdraws its troops from the territory of another party following the end of war because their mission has been accomplished, or their presence in the foreign territory has become untenable, or they are no longer welcomed by the host government.

Although public international law provides clear rules surrounding how wars end, there does not appear to be any rule applicable to the process of troop withdrawal following the end of a war.

By logic, one can reasonably posit that in the case of peace treaty or armistice agreement (as these agreements are essentially interstate contractual agreements) it follows that troop withdrawal process, if explicitly stated within the documents, would be carried out in a manner prescribed in the agreements.

On the other hand, in the case of ending a war by either implied mutual consent, debellatio, or unilateral declaration, it would also reasonably follow that any such troop withdrawal process would likely be carried out by the withdrawing party at their sole discretion.

The Case of U.S. Troop Withdrawal from Afghanistan

Given the above stated laws and assumptions, the question then becomes how should the United States have withdrawn its troops from Afghanistan?

An answer that is based on public international law principles would depend on whether the official end of the war occurred either through formal means or informal means.

The facts show that on Feb. 29, 2020, the U.S. signed the “Agreement for Bringing Peace to Afghanistan” (the Doha Agreement) with the Taliban, and set a May 2021 deadline for the withdrawal of all U.S. combat troops.

On the same day, the U.S. and the United Nations’ recognized government of Afghanistan issued a Joint Declaration reflecting some, though not all, of the terms of the U.S. agreement with the Taliban.

In the months following the Doha Agreement, the parties implemented some aspects of the terms of the agreement. But others remained unfulfilled, which culminated in an April 13, 2021, unilateral announcement by President Joe Biden to postpone withdrawal by almost three months (by Sept. 11, 2021), and leaving no room for additional extensions.

Assuming the Doha Agreement falls within the category of either a peace treaty or armistice agreement, then the manner of U.S. troop withdrawal – if such process was specifically stated in the document – would be legally binding from an international law perspective.

If, on the other hand, the Doha Agreement is not considered a peace treaty or armistice agreement – because at the time of negotiations the Taliban was not a United Nations’ recognized government – then the manner of U.S. troop withdrawal was carried out at U.S. discretion, and therefore was an informal means of ending the war still permissible under public international law.

Notwithstanding the legal theory, the facts seem to suggest that the agreement falls within the formal category, because the Biden administration has honored the Doha Agreement in every way, except for its decision to delay troop withdrawal until the end date of Sept. 11, 2021.

Conclusion: Another Perspective

Although there appears to be no neutral position when discussing recent U.S. troop withdrawal from Afghanistan following the end of the 20-year war, an approach based on international law principles provides an interesting perspective and may add an interesting dimension to the ongoing discussion.

Endnotes

¹ Covenant of the League of Nations, 1919, 1 International Legislation 1, id. (M.O. Hudson ed., 1931).

² ​See G. Schwarzenberger, “Peace Treaties before International Courts and Tribunals,” Indian Journal of International Law, 1968.

³ The texts of all the armistices of World War I are reproduced in A History of the Peace Conference of Paris, Appendix V (H.W.V. Temperley ed., 1920).

⁴ Michael N. Schmitt, “Debellatio” (October 2009), Max Planck Encyclopedia of Public International Law, 2009.