What were the reasons and justifications given at the time for why the allies only declared war on Nazi Germany when Hitler and Stalin both had invaded Poland?

by CosmicRaccoonCometh

Was the USSR justification that Poland had ceased to exist when Germany invaded simply repeated, or was there a different reasoning given to make sense of why they responded to the invasion by both Germany and USSR with a deceleration of war only on one of them?

scarlet_sage

You may be interested in these answers from the FAQ section "Soviet-Polish Relations" .

"Why is that only Nazi Germany is condemned for invading Poland while the Soviet Union also annexed a large portion of Poland and committed nearly half a million troops?" by /u/kieslowskifan
"Why did England and France only declare war on Germany while Russia invaded Poland too?" by /u/Balnibarbian
"Anglo-Polish Military Alliance Pact - did Britain and France fail to uphold their side of the pact?" by /u/Bro_Winky, seanisgod, and davratta.

But this is not to discourage more questions, data, or debate.