Quote Originally Posted by Sheogorath
Wikipedia gives the following:
The British Empire
The Kingdom of France
The United Provinces (Dutch Republic)
The Swedish Empire
The Ottoman Empire
The Kingdom of Prussia
The Russian Empire
The Spanish Empire
Polish-Lithuanian Commonwealth
Republic of Venice
The Thirteen Colonies

I'm not sure if those are 'confirmed' or not, though, but they would make sense.
Wait I though the Mughals were confirmed as well...