Answer
The Constitutional Crisis in Spain, which occurred during Rajoy's tenure from 2017 to 2018, was triggered by the Catalan independence movement. Catalonia, an autonomous region of Spain, held a referendum on independence in 2017, which the Spanish government deemed illegal. The Catalan government's subsequent declaration of independence led to the Spanish government imposing direct rule on Catalonia and arresting several Catalan leaders, escalating tensions and causing political turmoil.