The (Deutsche) Fürstenbund (German: [(ˈdɔʏtʃə) ˈfʏʁstn̩bʊnt], "[German] League of Princes") was an alliance of mostly Protestant princes in the Holy Roman Empire formed in 1785 under the leadership of Frederick II of Prussia. The alliance, which initially comprised the three major northern states of Brandenburg/Prussia, Hanover and Saxony, was set up officially to safeguard the constitutional integrity and territorial status quo of the Empire, but more immediately to oppose the long-cherished ambition of Joseph II to add Bavaria to the Habsburg domains.
Soon after he became sole ruler of the Habsburg lands at the death of his mother Maria Theresa in 1780, Joseph II revived an old ambition and entered into negotiations with Elector Karl Theodor of the Palatinate and Bavaria with the aim of trading Bavaria for the Austrian Netherlands. Had the plan been brought to fruition, the Habsburgs would have augmented their core domains with a large contiguous German-speaking territory while at the same time getting rid of far-away provinces that has proven to be difficult and costly to defend whenever Austria had been at war with France and/or Prussia. For Karl Theodor, his interest in the projected deal was mostly a matter of prestige as he envisioned himself as the ruler, possibly with the title of king, of a reconstructed Duchy of Burgundy composed of the Southern Netherlands plus his existing possessions in the Lower and Upper Rhine region, such as the Palatinate of the Rhine and the duchy of Berg-Jülich.
The rumored deal proved unpalatable both to the ambitious Frederick II, who saw himself as the foremost German monarch, and to the Electors of Hanover and Saxony who were disturbed by the far-reaching political and strategic implications of the projected territorial swap. Once they publicly declared their opposition though the creation of a Deutsche Fürstenbund, the rulers of lesser Protestant states, including Brunswick-Wolfenbüttel, Saxe-Gotha, Saxe-Weimar, Mecklenburg, Baden and Brandenburg-Ansbach, soon joined them. The Archbishop-Elector of Mainz, Archchancellor of the Empire, eventually gave his support, not least because it was known that Karl Theodor and Joseph II also mulled over the possible secularization of the Archbishopric of Salzburg, inconveniently wedged between Bavaria and Austria.
Joseph II was taken aback by the suddenness and strength of the opposition to his plan and after some minor sabre-rattling suspended his project. Having attained its true objective, the Fürstenbund gradually disintegrated and disappeared altogether after the outbreak of the French Revolution in 1789 and the death of Joseph II the year after.