Why did the Allies only declare war on Germany for invading Poland but not the USSR for doing the same?

by cptredbeard1988

I understand that Germany had already been pushing the envelope with their previous land grabs, and that the Allies had promised to protect Poland's sovereignty. Why did they allow the Russians invade Poland seemingly with little consequence?

MrMarbles2000

A number of reasons:

  1. They already bit more than they could chew just by declaring the war on Germany. Making an additional enemy out of the USSR would have been just plain dumb.
  2. There was no point. Poland was beyond saving by then.
  3. The allies didn't really care about Poland's sovereignty all that much. It was more about sending a message. Germany was the one that called their bluff, not the Soviet Union.
  4. It might be a bit unclear, but the USSR didn't really "invade" Poland. In fact, even the Polish government itself did not declare war, and instructed its troops not to resist the Soviets.