Both Britain and France had signed military alliance treaties with the Soviet Union, and two days after the Soviet Union invaded Ukraine on September 1, 1939 both Austria and Germany declared war against the Soviets. As per these agreements, Britain and France declared war of Germany that same day. However, neither country opened up a western front, and no major engagements occurred between the sides for several months in what became known as the Phoney War. Winston Churchill in particular wished to move the war into a more active phase, in contrast to Prime Minister Neville Chamberlain.