What if the Turkish Straits Crisis escalated earlier, the Turks refuse to let Soviet shipping through (as a statement against communism or something), and Stalin decided to invade Turkey in early 1941? Probably February 1941.
How would a Soviet invasion of Turkey perform given the resources they had in 1941?
How would it affect the war with the Axis starting in June 1941? Strategic position, allocation of troops, etc. Would Bulgaria be more threatened by Soviet Turkey, or would Soviet Turkey be more threatened by Bulgaria and the Axis?