The Sonderbund (meaning "separate alliance", in German), was a league created in 1845 in Switzerland between seven Catholic and Conservative cantons in order to protect their interests against a centralization of power.

The member cantons were: Lucerne, Fribourg, Valais, Uri, Schwyz, Unterwalden and Zug. Some liberal Catholic cantons such as Ticino and Solothurn did not participate.

This alliance was concluded after the Radical Party had taken power in Switzerland and had, thanks to the majority of cantons, taken anti-Catholic measures such as the closure of monasteries and convents in Aargau in 1841. When Lucerne, in retaliation, recalled the Jesuits the same year, groups of armed Radicals ("Freischärler") invaded the canton. This caused a revolt, mostly due to the fact that the elite in these rural cantons did not want to lose their privileges to a more centralized Switzerland.

The Radical majority in the Federal Diet decided to dissolve the Sonderbund on October 21, 1847. The confederate army was raised against the members of the Sonderbund. The army was composed of soldiers of all the other states except Basel-Stadt and Appenzell Innerrhoden (which had stayed neutral). General Guillaume-Henri Dufour led the army and defeated the Sonderbund in a campaign that lasted only from November 3rd to November 29th, and claimed fewer than hundred victims. He ordered his troops to spare the injured, anticipating the formation of the Red Cross in which he participated a few years later.

In 1848, a new constitution ended the almost-complete independence of the cantons and transformed Switzerland into a federal state. The Jesuits were banished from Switzerland.