Final answer:
The Nazi invasion of Poland, due to fabricated claims of Polish aggression and the strategic use of blitzkrieg tactics, significantly contributed to the start of WWII as it prompted Britain and France to declare war on Germany, honoring commitments to Polish sovereignty.
Step-by-step explanation:
Why the Nazi Invasion of Poland Started WWII
The Nazi invasion of Poland on September 1, 1939, was pivotal in sparking World War II. The Nazis used fabricated claims of Polish aggression and mistreatment of ethnic Germans as a pretext for the attack. This invasion was the culmination of aggressive expansionist policies by Nazi Germany under Adolf Hitler, who had earlier annexed Austria and the Sudetenland region of Czechoslovakia without provoking a military response from Western powers due to appeasement.
Hitler had long sought the return of the Polish Corridor, territory granted to Poland after World War I, which provided it with access to the Baltic Sea but separated East Prussia from the rest of Germany. The German invasion showcased the devastating effectiveness of blitzkrieg tactics, combining air and ground forces to encircle and devastate the Polish army. The swift conquest of Poland was followed by the Soviet Union's invasion from the east as per the secret protocol of the Nazi-Soviet Pact.
The direct military intervention by Germany in Poland finally compelled Britain and France to declare war on Germany, honoring their commitment to Polish sovereignty and marking the official outbreak of World War II. Although they declared war, Britain and France exerted little to no effective military assistance to Poland, which was overrun by the combined might of German and Soviet forces.