What was the sedition that occurred during the era of Uthman ibn Affan and led to the war between him and Ali, may Allah be pleased with them both?

There was no war between Ali and Uthman, may Allah be pleased with them both. Rather, the war was between Ali and Talhah and Az-Zubayr in the Battle of the Camel, and between Ali and Mu'awiyah in Siffin. Each party was a mujtahid (one who strives to reach a correct legal opinion), so the one who is correct receives two rewards, and the one who is mistaken receives one reward. One should refrain from delving into the disputes that occurred between them. For those who desire details, they should refer to books of history and creed.