an alliance or league that is formed by a group of people or entities with mutual support or a common goal in mind, often for some illicit or unlawful purpose;
e.g. The communities formed a confederacy to fight for their rights.
(noun)
the group of 11 American states that formally withdrew from the country in 1860 and 1861 (used as "Confederacy");
e.g. These states formed the Confederacy due to their shared beliefs.