Winds of War ww2

Quite coincidence, Sept. 1, 1939, started WWII poland - I got seeing this the same 

Sept. 1

https://www.youtube.com/watch?v=ocjEq6NcZOw

The Winds of War I - The Winds Rise (sa prevodom

Germany had a pact with Russia to occupy Poland between them, so how comes Britain only declared war on Germany and not Russia as well ? sounds like double standards to me....