Trialism in Austria-Hungary
In the history of Austria-Hungary, trialism was the political movement that aimed to reorganize the bipartite Empire into a tripartite one, creating a Slavic state equal in status to Austria and Hungary. Franz Ferdinand promoted trialism before his assassination in 1914 to prevent the Empire from being ripped apart by Slavic dissent.
Source: Wikipedia — Trialism in Austria-Hungary (CC BY-SA 4.0)