What is a confederation?

Confederation is  a group of people or nations form an alliance which is allowing each member to govern itself but agreeing to work together for common causes.

Explanation:

Allies opened a second front in Europe, but it was a long process that took years. Taking years to plan and come up with ideas on how they would do this, this got a code name called Operation Overload. By June 1944, almost 3 million troops were ready for the invasion. ... 4,000 ships filled with Allies invaded France.