The Saarland possessed little unity before the 20th cent. Until the late 18th cent. it was divided among France (which held the city Saarlouis and the adjacent territory), the county of Saarbrücken (a dependency of Nassau), and the palatine duchy of Zweibrücken. In 1797 it was ceded to France by the Treaty of Campo Formio. The Treaty of Paris of 1815 divided the territory between Bavaria (i.e., the Bavarian or Rhenish Palatinate) and Prussia. Industrial development in the area occurred after 1871, when Alsace-Lorraine became a part of the German empire. With Lorraine's iron ore deposits, the Saarland was able to take advantage of its extensive coal fields.
The Saar Territory came into existence as a political unit when the Treaty of Versailles (1919) made it an autonomous territory, administered by France under League of Nations supervision, pending a plebiscite to be held in 1935 to determine its final status. France also received the right to exploit its coal fields until that time. When more than 90% of the votes cast in the plebiscite favored its reunion with Germany, the Saar was restored (Mar., 1935) to German control and constituted the Saarland prov.
During World War II, Hitler incorporated it (1940) with Lorraine (annexed from France) into the province of Westmark. The scene of heavy fighting at the close of the war (1944–45), the Saarland was placed under French military occupation in 1945 and in 1947 was given an autonomous government. In a referendum (1947) the population voted for economic union with France, and in 1948 a customs union went into effect. Strong West German claims to the Saar, however, were a serious cause of friction in postwar Franco-German relations.
An agreement between France and West Germany in 1954 (see Paris Pacts) provided for an autonomous Saar under a neutral commissioner to be named by the Western European Union; the economic union with France was to be maintained for 50 years. However, the agreement was rejected (Oct., 1955) by the Saarlanders in a popular referendum, and, in accordance with subsequent Franco-German agreements (1956), the Saar Territory became (Jan. 1, 1957) a state (as Saarland) of the Federal Republic of Germany. The agreements permitted France to extract coal from the Warndt deposit until 1981, but the customs union with France was dissolved in July, 1959, whereupon the Saarland became economically integrated with West Germany (now Germany).