Too afraid to ask

by Thegreatsigma

If Poland has been invaded by Germany AND the Soviet Union in September 1939, then why have France and the UK declared war on Germany only and not USSR?

silverappleyard

Not to discourage further discussion, but you might be interested in this previous answer:

Why did France and Great Britain not also declare war on the Soviet Union for invading Poland in 1939? by u/Georgy_K_Zhukov