Semi-OT: Why didn't Britain and France declare war on Soviet Union in 1939 when it attacked Poland (and joined Germany in doing so)?
I have read really a lot of historic books and I own quite a large collection of them as well but I don't recall ever finding the proper explanation for the above...
Does anyone here knows something more about this issue?
Agreement of Mutual Assistance between the United Kingdom and Poland
London, August 25, 1939.
"Should one of the Contracting Parties become engaged in hostilities with a European Power in consequence of aggression by the latter against that Contracting Party, the other Contracting Party will at once give the Contracting Party engaged in hostilities all the support and assistance in its power."
Yale Law School - The Avalon Project (Documents in Law, History and Diplomacy)
http://avalon.law.yale.edu/wwii/blbk19.asp
Leo "Apollo11"