The North didn't start the war, the South did ... they had no right to secede and we should be thankful the North did win ... I don't know of any country split down the middle that has survived as two separate entities without a Civil War (look at the remnants of Persia) ... the Civil War certainly wasn't about slavery (although slavery was the catalyst) it was about Union (and the Union side won) ... Lincoln had extraordinary powers as president (but he was also the only president to have to manage the country in the midst of a Civil War) ... and he even held an election during the war (if he had been the tyrant you accuse him of being he wouldn't have done that ... and he had many advisers suggesting there not be an election)
By that logic, the US had no right to secede from Britain.