After the Soviet invasion of Poland in 1939 the Soviets effectively broke off diplomatic relations when they withdrew recognition of the Polish government at the start of the invasion. Up to 1.5 million Polish citizens, including over 200,000 Polish prisoners of war, were deported from Soviet-occupied Poland by the NKVD to the Gulags. Polish-Soviet diplomatic relations were re-established in 1941 after the German invasion of the Soviet Union forced Joseph Stalin to look for allies. Thus the military agreement from August 14 and subsequent Sikorski-Mayski Agreement from August 17, 1941, resulted in Stalin agreeing to declare all previous pacts he had with Nazi Germany null and void, invalidate the September 1939 Soviet-German partition of Poland and release tens of thousands of Polish priso