The only answer you can give, the one that makes the most sense, is the first one. Stalin and the Russians were carrying the load of war far beyond what should have been their share. Lenningrad had been under seige for nearly 900 days and Stalingrad was one of the bloodiest battles of the war.
Only 600 were left standing in what was one of the costliest battles in the pacific front. The japanese were the most affected with heavy casualties and suicide cases.
