The Clone Wars (22–19 BBY), also known as the Clone War and the Great Clone War, was the name given to the major galactic conflict fought between the Galactic Republic and the Confederacy of Independent Systems. The war was named after the clone troopers utilized by the Republic against the battle droid forces of the Separatists. These armies, the Grand Army of the Republic and the Separatist Droid Army, were two of the largest ever pitted against each other in galactic history, and the fighting between them rapidly spread to countless inhabited worlds.
Beginning with the First Battle of Geonosis, both sides scored significant victories over the other, and at different times during the war either seemed likely to triumph. The first two years of the war saw both sides skirmish with and raid each other, while fighting a handful of significant battles and trying to gain allies while they built up their respective war industries. A series of Republic defeats in the war's second year culminated in Operation Durge's Lance, a major strike into the Core Worlds led by the Supreme Commander of the Droid Armies,General Grievous. After the defeat of Grievous' forces in the Core, however, the Republic gained traction when it mobilized its greater industrial base. Using superior numbers, the Republic drove Separatists from the Core and Colonies and engaged them in their own territories, a series of attritional campaigns known as the Outer Rim Sieges. In an effort to reverse the course of the war, Grievous launched a massive strike on Coruscant through the Deep Core. Much of the Confederate fleet was lost and their Head of State Count Dooku was killed over Coruscant. General Grievous was subsequently killed at the Battle of Utapau. This, coupled with the issuing of Order 66 and the deactivation of the droid army, brought an end to the fighting. At the time, it was the largest galactic conflict to date.
Unbeknownst to most of those involved, the conflict was started, maintained, and eventually ended by the Dark Lord of the Sith Darth Sidious, whose ultimate goal was the transformation of the Republic into the Galactic Empire with him as Emperor as well as the eradication of the Jedi Order through the Great Jedi Purge. The conflict led to the Order of the Sith Lords controlling the dominant galactic government.
(Source Star Wars wiki)