Military Action to Recover Occupied Land: Lawful Self-defense or Prohibited Use of Force? The 2020 Nagorno-Karabakh Conflict Revisited

In September 2020, heavy fighting erupted between Armenia and Azerbaijan in and around Nagorno-Karabakh, a region of Azerbaijan long controlled by Armenia. After two months of military confrontations, a tripartite ceasefire was concluded, drastically altering the pre-existing territorial status quo.

The "Second Nagorno-Karabakh War" brings to light a fundamental question for international law on the use of force—and one that has received limited attention in legal doctrine. The question is this: when part of a State’s territory is occupied by another State for an extended period of time, can the former still invoke the right of self-defense to justify military action aimed at recovering its land?

The present article provides a broad appraisal of this question, examining the arguments for and against. In particular, it examines the conditions of self-defense—and whether occupation might be construed as a “continuing” armed attack. It subsequently addresses the relevance of the principle of the non-use of force to settle territorial disputes as well as the role of armistice and ceasefire agreements, before turning to relevant State practice. Ultimately, the authors agree with the Ethiopia Eritrea Claims Commission that “any exception to the prohibition of the threat or use of force for territory that is allegedly occupied unlawfully would create a large and dangerous hole in a fundamental rule of international law.”