Who were the two groups fighting against each other during the war of 1812?

Well, I don't know which war you are exactly talking about or which country but I assume it is about the war in 1812 between US and UK. If so, my answer would be:

The War of 1812 (1812–1815) was a conflict fought between the United States, the United Kingdom, and their respective allies. Historians in Britain often see it as a minor theatre of the Napoleonic Wars. However, in the United States and Canada, it is seen as a war in its own right.