What is the difference between confederacies and unitary types of governments?

A confederacy or federation is a group of independent powers united in common interest. This is how the United States began, as a confederacy of sovereign states. A unitary government is a single government that has total control over a single country, with smaller government branches merely being an extention of the central government. One may argue that the United States Federal Government of today has more in common with a unitary government than it's name would imply.