AHC: Prolong & Complicate the American Civil War

Okay, so we have another America scenario today

Our basic goal is twofold:
  1. Make the American Civil War last longer
  2. Get more factions involved, either by creating splinter factions or by foreign intervention
How do we accomplish this?
Probably not realistic, but fun though experiments:

Some Radicals decide Lincoln's not strict enough on slavery and succeed in instigating a slave revolt in some part of the South. Add in enough atrocity propaganda and Copperhead outrage and maybe the British/French intervene to prevent a second St. Domingue.

McClellan wins in 1864, but Unionist diehards with support of some of the army attempt to continue the war despite McClellan's overtures, probably alongside some sort of coup/power grab. A three-way conflict ensues between a re-invigorated Confederacy, McClellan's government, and the anti-McClellan faction.