Other forms: confederacies
A confederacy is a political union. The most famous American confederacy consisted of the southern states who fought the northern states in the American Civil War.
When you confederate — that is, join together for a common purpose — what you get is a confederacy. Americans will never forget a well-known but ill-fated confederacy, the Confederate States of America: an unrecognized state that formed in 1861, uniting the slave states that left the United States at the time of the Civil War. Any such political union could be called a confederacy (or a federation). When you see the word confederacy, think of togetherness in the political realm.