The Schlieffen Plan was Germany's pre-war strategic plan for fighting a potential war against both France and Russia.

It was developed by German Field Marshal Alfred von Schlieffen.

The plan's core assumption was that Russia would be very slow to mobilize its large army.

Therefore, the strategy was to launch a massive, rapid invasion of France first, knocking it out of the war quickly.

After defeating France, the German army would then be moved by rail to the east to confront the slowly mobilizing Russian army.

To achieve a quick victory over France, the plan required the German army to invade by marching through neutral Belgium, bypassing the heavily fortified French-German border.

The invasion of neutral Belgium was a key factor in Britain's decision to enter the war.

The plan was put into action in August 1914 but ultimately failed.

Its failure was due to stronger Belgian resistance, a faster-than-expected Russian mobilization, and tactical modifications that weakened the main German attack.

The failure of the Schlieffen Plan led to the stalemate and trench warfare of the Western Front.