Remilitarization of the Rhineland

The remilitarization of the Rhineland by the German Army took place on 7 March 1936 when German military forces entered the Rhineland. This was significant because it violated the terms of the Treaty of Versailles and the Locarno Treaties, marking the first time since the end of World War I that German troops had been in this region. The remilitarization changed the balance of power in Europe from France towards Germany, and made it possible for Germany to pursue a policy of aggression in Eastern Europe that the demilitarized status of the Rhineland had blocked until then.

Under Articles 42, 43 and 44 of the 1919 Treaty of Versailles—imposed on Germany by the Allies after the Great War—Germany was "forbidden to maintain or construct any fortification either on the Left bank of the Rhine or on the Right bank to the west of a line drawn fifty kilometers to the East of the Rhine". If a violation "in any manner whatsoever" of this Article took place, this "shall be regarded as committing a hostile act...and as calculated to disturb the peace of the world". The Locarno Treaties, signed in October 1925 by Germany, France, Italy and Britain, stated that the Rhineland should continue its demilitarized status permanently. Locarno was regarded as important as it was a voluntary German acceptance of the Rhineland's demilitarized status as opposed to the diktat (dictate) of Versailles. Under the terms of Locarno, Britain and Italy guaranteed the Franco-German border and the continued demilitarized status of the Rhineland against a "flagrant violation" without however defining what constituted a "flagrant violation". Under the terms of Locarno, if Germany should attempt to attack France, then Britain and Italy were obliged to go to France's aid and likewise, if France should attack Germany, then Britain and Italy would be obliged to Germany's aid. The American historian Gerhard Weinberg called the demilitarized status of the Rhineland the "single most important guarantee of peace in Europe" as it made it impossible for Germany to attack its neighbors in the West and as the demilitarized zone rendered Germany defenseless in the West, impossible to attack its neighbors in the East as it left Germany open to devastating French offensive if the Reich tried to invade any of the states guaranteed by the French alliance system in Eastern Europe, the so-called Cordon sanitaire.

...
Wikipedia