Original: In 1438 Trevi passed under the temporal rule of the Church as part of the legation of Perugia, and thenceforth its history merges first with that of the States of the Church, then (1860) with the united Kingdom of Italy.
Simplified: In 1438 Trevi became part of the lands belonging to the Church as part of the "legation" of Perugia: after that Trevi's history was as part of the States of the Church, then (1860) of the united Kingdom of Italy.