World War II began in Europe when German forces invaded Poland, employing a new military strategy known as 'Blitzkrieg' (Lightning War). This tactic emphasized speed, surprise, and overwhelming force, using coordinated attacks by armored tank divisions (Panzers) supported by close-air support from the Luftwaffe. The goal was to bypass enemy strongpoints and encircle armies, causing a rapid collapse of command and communication. Contrary to the slow-moving trench warfare of WWI, the Polish army was overwhelmed in weeks. On September 17, the Soviet Union invaded from the east, fulfilling the secret terms of their pact with Germany. The fall of Poland prompted Great Britain and France to declare war on Germany, though they were unable to provide direct military aid to the Poles in time.