The 1939 Battle of Warsaw, also known as the Siege of Warsaw, was a battle fought between Poland, heavily garrisoned and entrenched in the capital, Warsaw, and the German, Soviet and Czechoslovak Armies. The battle started on September 13, 1939, and ended on December 7, 1939.

The Battle of Warsaw was a last stand by the Second Polish Republic, which was heavily outnumbered by the Axis and lacked equipment. Despite these deficiencies, the Poles had been preparing Warsaw for battle since 1938, and defenses were extremely strong. Though the battle concluded in an Axis victory and the end of the Second Polish Republic, it is often considered a Pyrrhic victory - the Axis lost almost half a million troops and spent three months to ultimately capture a city that had been evacuated and completely destroyed. The long battle also allowed the Polish Army outside of Warsaw to escape from occupied Poland before the Axis could consolidate its control, fleeing through neutral Lithuania and then-neutral Romania, and it allowed Britain, France and the British Commonwealth extra time to reinforce and prepare before the beginning of the Battle of France.

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