The Galactic Civil War, also known as "When Star Wars Was Good," was a major galactic conflict between the north and south side of the galaxy. The war occurred when the north side of the galaxy was planning on passing a law that would take away the... oh wait, my bad, I am thinking of something else. The Galactic Civil War was really a conflict between the
badass oppressive Galactic Empire and some losers. It was one of the largest, biggest, darkest, and most important event in galactic history until the Expanded Universe was invented.
Normally the empire would win, but since Lucas is such a kiss ass to the good side, he decided to be nice and let the rebels win.