Answer:
The act of separating from a nation and becoming independent is called secession or declaration of independence.
Explanation:
According to https://en.wikipedia.org/wiki/Secession, secession or declaration of independence is the withdrawal of a group from a larger entity, especially a political entity.
It is a process that begins when a group proclains the act of secession or declaration of independence; it may be a peaceful or violent movement, but its outcome is a new political entity, totally independent.
