After the failure of the Munich Agreement, Britain and France pledged to defend Poland's independence.

In August 1939, Nazi Germany and the Soviet Union shocked the world by signing a non-aggression pact.

The Nazi-Soviet Pact contained a secret protocol that divided Poland and the rest of Eastern Europe into German and Soviet spheres of influence.

This pact ensured that Hitler would not have to fight a two-front war if he invaded Poland.

On September 1, 1939, Germany invaded Poland from the west.

The German invasion used a new military tactic called 'Blitzkrieg' ('lightning war'), which combined overwhelming air power and fast-moving armored divisions.

The Polish army, though it fought bravely, was quickly overwhelmed.

On September 3, 1939, in response to the invasion, Great Britain and France declared war on Germany.

On September 17, the Soviet Union invaded Poland from the east, fulfilling the terms of the secret protocol.

The invasion of Poland marked the beginning of World War II in Europe.