An act of annexing, or territories that have been annexed.(noun)
A legal merging of a territory into another body.(noun)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "annexation" in a sentence
"I happen to think that annexation is the real policy of the present Israeli administration only that they hope to achieve that result by stealth rather than by an outright declaration."
"What will follow next will depend on how strong Russia feels, how weak and slow the West's response is, but annexation is not out of the question."
"The impact of annexation is pretty foggy, however, except as it concerns the DOT facility being built on that parcel of land."