The instrument of union was signed by envoys of the cathedral chapter, the episcopal Ministerialis, the city of Chur and the districts of Domleschg, Schams, Oberhalbstein, Oberengadin, Unterengadin and Bergell.

In Trun, on 16 March 1424, a governing federation was established, comprising: Even before 1440, the lordships of Löwenberg, Thusis, Tschappina and Heinzenberg joined the League, despite the count of Werdenberg-Sargans having forbidden them from doing so.

After 1499, the Free State de facto separated from the Holy Roman Empire and developed, during the 16th century into a political entity that was unique in early modern Europe.

Additionally church leaders could no longer appoint secular officers, the monasteries were placed under government oversight and various tithes were abolished or reduced.

With the invasion of Switzerland by the French Revolutionary Armies, the Three Leagues were absorbed into the Helvetic Republic, as the canton of Raetia.

However, having permanently been detached from the Leagues after Revolutionary France fomented revolt there, the districts were annexed to the Cisalpine Republic on 10 October 1797.

The districts subsequently joined the Austrian client kingdom of Lombardy–Venetia after the Congress of Vienna and eventually become the Italian province of Sondrio.

The town of Campione was similarly detached from the Landvogtei of Lugano at the same time, leading to its current position as an Italian enclave within Ticino.