The Second Clone Wars, also known as Clone Wars II, was a galaxy-wide conflict originally between the three greatest forces at that time. As the galactic community was aware of, the three combatants were the Galactic Republic, with the Great Clone Forces serving as its military, the Federal Society and the Dark Empire. Bursting into eruption in the year 57 ABY, the War, as what it was referred to as during the historic wartime, went on for four straight years until it ended in 61 ABY.
It was said to be the sequel to the Clone Wars which occurred decades before, earning the war its name. As calculated by the Republic’s historians, the conflict had caused an estimation of over six billion deaths across the galaxy, excluding the number of clone troopers killed in the war. Another great effect of the war was the destruction of over three hundred planets, regardless of being inhabited or otherwise.
When the war was nearing its end, a Sith Lord, who had secretly rewritten several orders for the clone army, killed the Supreme Chancellor. Imposed as the now deceased Chancellor, the Sith began issuing Order 51, an act that ordered for the entire clone army to destroy the Jedi and later on exterminate themselves, thus bringing the war closer to its end.
The remaining Grand Army of the Republic proceeded to crush enemy lines until they triumphantly gained victory over the conflict. Thousands of Sith now crept into the Republic, quickly giving the Sith Empire total control of the galaxy. The Sith Chancellor immediately became the actual Supreme Chancellor of the new Dark Republic.
Unbeknownst to the Republic, around six thousand clone troopers were defective to the order and developed an underground community. The clones soon came out of hiding and rose up in the Clone Uprising as the Clone Rebel Alliance against the government they once obeyed. Having been discovered by the Republic, the clone rebels assaulted Coruscant in a failed attempt to assassinate the Supreme Chancellor, thus triggering the Third Clone Wars.