The most common and most likely answer to this crossword clue is the 10 letter word ANNEXATION
A
N
N
E
X
A
T
I
O
N
Buddy explains!
The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ANNEXATION mean?
ANNEXATION noun- Addition or incorporation of something, or territories that have been annexed.
- A legal merging of a territory into another body.