Tito was a very charismatic leader. Since he was neither Serbian nor Croatian, he stood the best chance of holding the republic together after the war was over. Furthermore, the Western Allies hadn't supported Mihailovich during the war to the same degree -- in terms of weapons, food and other supplies -- that the Soviets had supported Tito. The regrettable result was that Tito was in an overwhelmingly superior position to take control after the war, and there was nothing the State Department could have done about it.
Many fliers went down en route to and from Ploesti. Our State Department advised wounded aircraft to ditch in the half of the country controlled by Tito if possible. Most that did didn’t survive. Those that landed in Mihailovich’s sector were saved. Our airmen, upon returning to the US, attempted to intercede on Mihailovich’s behalf, knowing he was scheduled to be executed by Tito. Our State Department told these airmen to pound sand.