The Schlieffen Plan was implemented by Germany in a war for which it was not intended.

The war between France and Prussia took place in 1870-1871. Several major battles took place, with the Germans victorious and the French defeated, losing some territory. During this war, Prussia managed to unite the disparate German states, and its King Wilhelm became the first Emperor (Kaiser) of Germany.
He and his entourage understood perfectly well that Paris would not accept territorial losses, making a new conflict inevitable. At the same time, the French understood that the Germans would try to nip the threat in the bud by attacking first, so they began building powerful defensive fortifications along the border with Germany.
Berlin was indeed planning an attack on France, so the French defensive line on the border posed a serious problem. A solution was found by the Chief of the German General Staff, Field Marshal Alfred von Schlieffen. This commander proposed not to storm the fortified border, but to invade France through Belgium. A relatively small number of German covering troops would be stationed at the border. The French, whose main forces would be trapped in a pocket, would be routed within five to six weeks.

There were many opponents of the Schlieffen Plan in Germany. For example, some German diplomats considered an attack on neutral Belgium unacceptable. The military, however, welcomed the plan.
The French noticed the Germans building roads and bridges to the Belgian border, but they didn't take these preparations seriously. Despite this, the German blitzkrieg plan was never implemented as planned. Schlieffen was no longer alive by the start of World War I—he died in 1913. In his place, the German General Staff was headed by Helmuth von Moltke the Younger, who considered his predecessor's plan too bold and risky, so almost all German troops remained on the French border. Thus, the German commander made his own adjustments to the Schlieffen Plan, which practically nullified it.

As a result, the war became long and drawn-out for Germany, and was fought on two fronts, since Russia, an ally of France and Britain, also participated in the war.
But the Schlieffen Plan was ultimately implemented, albeit not in the war for which it was conceived. It was implemented by Hitler's troops, who quickly defeated France in 1940.
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