Finally, in the 17th Century, she tried to regain it. The Chief Minister, Cardinal Richelieu, described it as “the limits which nature has traced.” The Sun-King (Louis XIV) tried to obtain it by wars of aggression, and his forces managed to reach the upper Rhine. In 1648 by the Treaty of Westphalia, South Alsace was gained, followed by North Alsace in 1697 with the Treaty of Rijswijk. The Lower Rhine remained in German hands.
In 1792, the new French Republic took up the challenge. The French Revolutionary leader Danton described the river as being “marked out by nature” as France’s frontier. In 1787, the army of the new French Republic reached the Lower Rhine and established the puppet Cisrhenian Republic, which was annexed to France in 1802 giving her the desired natural frontier. It was not to last. In 1813, having been defeated by the Allies at the Battle of Leipzig, Napoleon crassly rejected peace terms offering recognition of the Rhine frontier in exchange for French evacuation of trans-Rhenian Germany. He fought on and lost. The ensuing Treaty of Vienna in 1815 reduced France to her pre-Napoleonic frontiers, so she lost the Lower Rhine, retaining only Alsace on the Upper Rhine. The Rhineland was ceded to Prussia, to keep France weak by having German forces stationed on her side of the river which was her geographical defence.
France paid the price. Deprived of “les limites naturelles”, in 1870, 1914 and 1940 she was invaded from the Rhineland. This could have and should have been avoided. In 1866, the Emperor Napoleon III missed a golden opportunity to conquer the Rhineland, by stabbing Prussia in the back while she was warring against the Austrian Empire. After the First World War, France occupied the Rhineland and established a short-lived puppet Rhenish Republic at Aachen. By the Treaty of Versailles in 1919, however, she he was induced to allow the Rhineland to remain part of Germany, under Allied military occupation for twenty-five years (1920-1935) and thereafter to be demilitarised ie off-limits for German forces. In violation of the Treaty, in 1936 Hitler sent his army into the Rhineland. It had sealed orders to retreat if the Allies took action. Laval, the weak French Prime Minister, took none, and France lost its last opportunity to keep the Germans out. In 1940 they swept through France from the Rhineland.
If France had permanently gained the Rhine frontier, she would have been secure from invasion and retained her position as the pre-eminent world power. In the Middle Ages, French was lingua franca of Europe, being the language of heraldry and courtly love. It was the official language of England from 1066-1346 as well as being the language of the Crusader Kingdom of Jerusalem (1099-1291), and also became the language of diplomacy. All communications between foreign ministries and embassies were in French until 1945. The League of Nations conducted its business in French, and therefore its seat was at Geneva in the French-speaking part of Switzerland. All this ended because France was invaded and conquered from the Rhineland in 1940. She had to be liberated by American forces in 1944, and the United States became thereby the master of the Western World, establishing the United Nations at New York with English as its language, because Americans could not speak French, (Spanish being their second language). English replaced French as the world’s diplomatic language, and the United States replaced France as the cultural fountainhead of the Western World.