Muhammad was a prophet who got messages from God, he was the ruler of the new Arab nation founded by himself, he was the supreme judge and he was the supreme commander of the army of the Arab nation. The Arab nation founded by prophet Muhammad was the absolute theocratic state. The only parallel for this theocratic state was kingdom of Egypt under Pharaohs and the Holy roman empire. In Egypt the king claimed to be the God himself. But Muhammad claimed to be only messenger of the God. In the holy roman empire the ruler and head of the religion were different persons. The ruler became subordinate to the head of the religion. But in the first Arab nation Muhammad was both the ruler and and the head of the religion. Here is the origin of the political Islam.
In modern era the kingdoms are secular. So believers of the Islamic faith shed off all the political content of their religion including the criminal and civil Sharia' laws.