In simple terms

Annexation is a state declaring that territory it holds by force is now legally its own. The claim is about sovereignty, the recognized legal title to land, not merely about who has troops on the ground.

International law treats that claim as void. Force can change who controls territory; the modern rule is that it cannot change who holds title to it.

How it works

Annexation usually follows occupation. A state takes territory militarily, then announces that the land has become part of its own, sometimes after a vote organized under its control.

Two rules block the move. Article 2(4) of the UN Charter requires members to refrain from the threat or use of force against the territorial integrity or political independence of any state. [3] The 1970 Declaration on Friendly Relations speaks directly to title: the territory of a state shall not be the object of acquisition by another state resulting from the threat or use of force. [2]

Then comes the duty of non-recognition, the obligation on other countries not to treat the acquisition as legally valid. In practice their maps, treaties and embassies keep working from the old border, which denies the annexing state the legitimacy it wanted. [2]

The prohibition applies whether the territory was taken in a war of aggression or in self-defense. [1]

Why it matters

The ban on taking land by force is one of the load-bearing rules of the order built after 1945, and the Security Council has affirmed the inadmissibility of acquiring territory by war in a series of resolutions beginning with Resolution 242 in 1967. [1] If one annexation were accepted, every contested border would turn into a question of who is stronger.

The label also decides which law applies. Occupation does not transfer sovereignty, so an occupying power holds temporary and limited authority; annexation asserts permanence instead. [2]

Where you will see it

• Security Council and General Assembly debates on territorial disputes [1]
• Government statements refusing to recognize a new border [1]
• Legal analysis separating occupation from annexation [2]
• Accounts of the Stimson doctrine of 1932, a policy of refusing recognition to territory taken by aggression [2]

Example

Most governments kept the old boundary on their official maps, because recognizing the annexation would have accepted a transfer of sovereignty made by force.

Often confused with

Occupation is military control of territory without legal title, and it is regulated rather than banned. Annexation is the claim to title itself, and it is prohibited. [2]

This entry explains a legal term. Laws differ by country and change over time. It is not legal advice.

Editorially reviewed by Specialty Digest Editorial TeamLast reviewed September 28, 2026Researched and drafted with AI assistanceReport an issue