 But the March 1939 annexation of rump Czechoslovakia, in violation of the Munich Agreement signed only months before, forced a change in Franco-British policy from an emphasis on avoiding war (Appeasement) to an emphasis on war preparation, of which an important feature was the declaration of Franco-British guarantees of Polish independence.When Germany invaded Poland in September 1939, Britain and France declared war (3 September 1939).Hitler's strategy for war was laid out in "Mein Kampf" (1925/1926).