The region around the Saar River and its tributary valleys is a geologically folded, mineral-rich, ethnically German, economically important, and heavily industrialized area.

The region had been previously annexed by France (as the Bailiwick of Sarrelouis [fr], 1685) and occupied during the Revolution (1790–1798) and the Napoleonic Wars, when it had been included in the First French Empire as the Sarre department between 1798 and 1814.

In 1920, Britain and France established a nominally independent occupation government for the League of Nations mandate of the Saar: the greater part of the area under its control was carved out of the Prussian Rhine Province and was supplemented by two Bavarian districts (Homburg and St. Ingbert) taken from the Rhenish Palatinate.

On 13 January 1935, a plebiscite held in the territory at the end of the 15-year term, resulted in 90.7% of voters casting their ballot in favour of a return to Germany, and 0.4% voting for union with France.

In 1942 it was renamed Westmark (Western March), as it was planned to be expanded to incorporate parts of German-occupied French Lorraine which, however, did not materialise.

In July 1945, two months after World War II had ended in Europe, the Allied forces were redeploying from the areas they had conquered into their respective zones of occupation.

December 1947 had severe flooding along the Saar river, water higher than in the past 150 years, with extensive relief efforts undertaken.

As part of this policy, limits were placed on permitted production levels, and industries in the Saar were dismantled as they had been in the Ruhr, although mostly in the period before the detachment (see also The 1949 letter from the UK Foreign minister Ernest Bevin to the French Foreign minister Robert Schuman, urging a reconsideration of dismantling policy).

[6] With the participation of West Germany in the ECSC, agreement on termination of the International Authority for the Ruhr came into force on 25 June 1952.

[citation needed] In the Paris Agreements of 23 October 1954, France offered to establish an independent "Saarland", under the auspices of the Western European Union (WEU), but a referendum held on 23 October 1955 rejected this plan by 67.7% to 32.3% (out of a 96.5% turnout: 423,434 against, 201,975 for) despite the public support of West German Chancellor Konrad Adenauer for the plan.

West Germany agreed to the channelization of the Moselle, which reduced freight costs for the French steel industry in Lorraine.

West Germany also agreed to the teaching of French as the first foreign language in schools in the Saarland; although no longer binding, the agreement is still generally followed.

The treaty also stated that economic union with West Germany was to be completed by 1960, with the exact date of the replacement of the Saar and French franc by the Deutsche Mark being kept a secret called "Day X" (Tag X).

As a footnote to the creation of the European Union, the territorial dispute over control of the Saarland was one of the last between member states and led to the European flag being given a politically neutral ring of twelve stars rather than the originally proposed 15 (one of which was to represent a nominally independent Saar as a member of the Council of Europe).