The First Republic is the first galaxy-wide government of the Milky Way Galaxy.
It was a representative democracy where each race contributed an equal part of the military, as they were able. Eventually, as a result of corruption, several races were allowed to gain massive military power, and began to use it to pressure others.
When the rest of the Republic tried to stop them, it fell into a civil war that lasted decades, caused unbelievable devastation, and killed a large part of the advanced races in the galaxy. In the aftermath of the ancient war, a new galactic government, the Galactic Union, rose.