Answer:
A confederation is voluntary, while the membership in a federation is not.
Explanation: Sometimes confederation is mistakenly thought as another word for federation. But they are different, Confederation is Held by the member states, while Federation is held by the federal government. The Central Authority of Confederations usually have a weak group arranged by the member states, While a federation's central authority is different, it has, like the name sounds, A federal government that governs the member states.