The Fourth Crusade (1202–1204) was originally intended to conquer Muslim-controlled Jerusalem by means of an invasion through Egypt. Instead, in April 1204, the Crusaders of Western Europe invaded and conquered the Christian (Eastern Orthodox) city of Constantinople, capital of the Eastern Roman Empire (Byzantine Empire). This is seen as one of the final acts in the Great Schism between the Eastern Orthodox Church and Roman Catholic Church.

The crusaders established the Latin Empire (1204–1261) and other "Latin" states in the Byzantine lands they conquered.