The Treaty of Fontainebleau (German: Vertrag von Fontainebleau) was signed on 30 May 1631 between Maximilian I, Elector of Bavaria, and the Kingdom of France. The accord established a secret alliance between the two Catholic states during the Thirty Years' War.
The treaty, which was to be valid for eight years, called for French military assistance in case of an attack on Bavaria. France also confirmed Bavaria's possession of the Upper Palatinate and status as an electorate. For his part, Maximilian promised not to support France's enemies, such as the Imperial forces of the Austrian Habsburgs.
The treaty proved worthless in 1631, as the Protestant King Gustavus Adolphus of Sweden (allied with France) attacked Bavaria, which did not receive French aid. France argued that Bavaria had initiated conflict with Sweden, and as such had nullified the treaty. In actuality, French aid to both Sweden and Bavaria would have been counterproductive. Cardinal Richelieu of France had been under the impression that Sweden would respect Bavaria's neutrality during Sweden's war against the Habsburgs. Because the Treaty of Fontainebleau had failed to provide security for Bavaria, Maximilian allied his state with the Imperial party of Vienna.
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