Annexation has often been seen, quite naturally, as linked to aggression. Many international lawyers have propounded the principle that unilateral acts inconsistent with fundamental rules of international law should be viewed as null and void, and no prescriptive rights should accrue in favor of the aggressor. Thus, annexation resulting from aggression should not be recognized. Yoram Dinstein raises the interesting question of the long-term effectiveness of the legal principle of nonrecognition. “If the de facto control of the territory annexed by the aggressor continues uninterrupted for generations, the non-prescription rule may have to give way in the end. International law must not be divorced from reality.”
What if an occupation arises, not from an act of aggression, but following a defensive war in which a state defending its territory occupies neighboring lands? This is one factually well-grounded view of the position of Israel regarding the territories occupied since 1967. In certain parts of these territories (the Golan Heights, and East Jerusalem with extended boundaries) subsequent acts of annexation or quasi annexation have been taken, mainly in the form of applying Israeli law to them. The overwhelming tendency of states and international bodies has been not to recognize these purported annexations but, rather, to view the law on occupations as remaining applicable to the situation. The general prohibition on annexation, in other words, continues to be seen as a key principle, even though it is under pressure.
Adam Roberts, “Transformative Military Occupation: Applying the Laws of War and Human Rights”, The American Journal of International Law, Vol. 100 (2006), 584.