The Republic since its defeat of the Empire and it's Death Star has seen many wars and skirmishes with it's eternal counterpart. During the years of the Battle of Empress Teta, many of the Republic allies and planets within the Senate broke free and formed under their own powers and governments. The Republic has several basic subcategories to it including and not limited to the Military, Senate, and Civilian.
The Empire since it's original defeat of the second Deathstar has been going through the loss and gain of many planets - keeping its ironfisted hold on planets. When The Decay took place, they lost Coruscant and some of their forces that had been planning a mutiny. Peace talk ensued and when that broke down, they went to war again with the much weakened Republic.