"Three years of mounting international tension - encompassing the Spanish Civil War, the Anschluss (union) of Germany and Austria, Hitler's occupation of the Sudetenland and the invasion of Czechoslovakia - culminated in the German invasion of Poland on 1 September. Britain and France declared war on Germany two days later. While the USA proclaimed neutrality, it continued to supply Britain with essential supplies, and the critical Battle of the Atlantic between German U-Boats and British naval convoys commenced.
Western Europe was eerily quiet during this 'phoney war'. Preparations for war continued in earnest, but there were few signs of conflict, and civilians who had been evacuated from London in the first months drifted back into the city. Gas masks were distributed, and everybody waited for the proper war to begin.
In eastern Europe and Scandinavia, however, there was nothing phoney about the war. With the Ribbentrop Pact signed between the Soviet Union and Germany in late August, Russia followed Germany into Poland in September. That country was carved up between the two invaders before the end of the year, and Russia continued this aggression by going on to invade Finland."