A worldwide caliphate is a type of organization, or system of governing, in which all of the people in the world are governed by one leader. In this system, the leader would be like a king or an emperor. He or she would be responsible for making sure that all people everywhere treated each other kindly, obeyed the law, and got along with one another. In a caliphate, all of the people around the world would be united under one leader. This kind of system of ruling has never actually been tried in the world, but some people think it would be a peaceful way for everyone to live together.