What were the consequences of the Pact?

The public German-Soviet Nonaggression Pact caused consternation in the capitals of Britain and France. After Germany invaded Poland from the west on Sept. 1, 1939, Soviet troops invaded Poland from the east on September 17, meeting the advancing Germans near Brest-Litovsk two days later. The partition of Poland was effected on September 29; at this time the dividing line between German and Soviet territory was changed in Germany's favour, being moved eastward to the Bug River (i.e., the current Polish-Soviet frontier). The Soviets soon afterward sought to consolidate their "sphere of influence" as a defensive barrier to renewed German aggression in the east. Accordingly, the Soviet Union attacked Finland on November 30 and forced it in March 1940 to yield the Isthmus of Karelia and make other concessions. The Baltic republics of Latvia, Lithuania, and Estonia were annexed by the Soviet Union and were organized as Soviet republics in August 1940. The Nonaggression Pact became a dead letter on June 22, 1941, when Nazi Germany, after having invaded much of western and central Europe, attacked the Soviet Union without warning in Operation Barbarossa.

Source: Britannica Online