Answer: Confederation
Explanation: An association or union of independent states who align or come together voluntarily to achieve a common goal is called a Confederation. Each state of a Confederation is sovereign that is, they exhibit Supreme rule or authority within their state or jurisdiction.
However, member states of a Confederation are guided by a common law binding the states, Confederation also posses an internal government vested with certain authority or power over the member states all in a bid to maintain sanity and attain the purpose of the union.