Why did the former colonies want a written constitution? They wanted to have control over the government before any other states joined. For their own protection: they knew that as previous British citizens, the lack of a constitution meant that the laws and government could be changed by a few members of Parliament or manipulated by a shrewd Prime Minister. They wanted to have in writing what was expected of them. They wanted something to hang on the walls of their homes. For America's protection: they knew that British Parliament could change or manipulated the government.