Why did the Allies not declare war in 1939 on the Soviet Union? (Patreon)

Poland '39: Why no War against Soviet Union by the Allies?

“I know this is a sensitive issue, but it still bugs me and I have never been given an adequate answer. If Britain and France had guaranteed the military support of Poland, were they not also bound to declare war on the USSR, who invaded the other half of Poland, [more than two weeks later]*? Since this is not a strictly military history subject, that delves into politics as well, I will completely understand if you will not answer this.” *The original quote had a minor error that the poster himself corrected in a follow-up comment for simplicity I corrected it in the original quote. Follow-up quote was: "Oh and sorry about the error, it was just over two weeks later, on the 17th of September." Military Aviation Channel: https://www.youtube.com/user/Bis18marck70/ Cover design by vonKickass. Adaption of this image: https://commons.wikimedia.org/wiki/File:Churchill,_Stalin,_and_Harriman_at_Moscow_Converence,_August_1942_(24293784752).jpg  »» SUPPORT MHV «« » paypal donation - https://paypal.me/mhvis » patreon - https://www.patreon.com/join/mhv » subscribe star - https://www.subscribestar.com/mhv »» MERCHANDISE «« » teespring - https://teespring.com/stores/military-history-visualized » SOURCES « Jackson, Peter: Europe – The failure of diplomacy, 1933-1940. In: The Cambridge History of the Second World War, Volume II, UK, 2015. Nord, Philip: France 1940. Defending the Republic. Yale University Press: New Haven and London, UK, 2015. Alexander, Martin S.: French grand strategy and defence preparations. In: The Cambridge History of the Second World War, Volume I, UK, 2015. Imlay, Talbot: Western Allied ideology, 1939-1945. In: The Cambridge History of the Second World War, Volume II, UK, 2015. Kahn, Martin: ‘Russia Will Assuredly Be Defeated’: Anglo-American Government Assessments of Soviet War Potential before Operation Barbarossa, The Journal of Slavic Military Studies, 25:2 (2012). Kennedy, Paul: The War at Sea, in: Cambridge History of the First World War – Volume I. Das Deutsche Reich und der Zweite Weltkrieg, Band 2. #WW2 #Poland1939 #SovietUnion