Complex sentence: It has been a title for sovereign of grand principality, but is not in such use any longer, the last titular grand principalities having vanished in 1917 and 1918, the territories being united into other monarchies or introducing republican government.
Split into simpler sentences: It has been a title for the sovereign of a grand principality, but it is not in such use any longer. The last titular grand principalities vanished in 1917 and 1918, the territories being united into other monarchies or introducing republican government.