Galactic Alliance Defense Initiative

The Galactic Alliance Defense Initiative, otherwise known as the GADI, the Alliance, and sometimes the Clone Alliance, is one of the primary galactic powers in the FFA galaxy. 
It's existence came to be as a result of Order 66, the order which the Clone Army betrays the Jedi Order at the behest of Supreme Chancellor Palpatine, or Darth Sidious. However, thanks to blind luck in the form of Fleet Admiral Caden Forsyth, the truth is revealed and had entire Clone armies, like the 501st Legion, removed their biochips and swore loyalty to the Jedi and the Republic.
Unfortunately, one-third of the Clone Army continued their campaign in wiping out the Jedi. Following the Proclamation of the New Order, the Empire began the Great Jedi Purge, something which the Clone Armies loyal to the Republic were immediately against and began a campaign of their own, in which their aim is to overthrow the Sith-dominated Empire and restore freedom.
After the Galactic Civil War, the GADI supplements the former Empire, rivalling that of the New Republic as a galactic power. However, compared between the two, and with the rise of the First Order, the latter wants to supplant peace talks while their armed forces diminished throughout. The former had been weary of their actions and constantly upgraded both their ground forces and naval forces, waiting for the First Order to launch the strike.
When the former Emperor broadcasted his message, revealing the return of the Sith and the Final Order, the Alliance, aided by remnants of the New Republic, the NSC and allies from across the galaxy, joined the Resistance in one massive battle on Exegol, finally defeating Darth Sidious once and for all.