Most secession are peaceful. I would not expect a California or New England secession to start a war.
Ummmm.... Virtually every secession in the history of mankind was peaceful... but immediately followed up with a military response from the leadership that was just rejected. We peacefully declared Independence. The King didn't take it politely. The South peacefully declared nationhood. The North refused to leave SOUTH Carolina (hundreds of miles from their country), and eventually had to be removed with cannon fire. India declared independence, and the Brits killed tens of thousands of unarmed women and children before they were shamed into stopping.