Given the question: Question: "Which document needed to be implemented for the six self-governing colonies of Britain to form into one nation?"  Context: "In 1901, the Federation of Australia was the process by which the six separate British self-governing colonies of New South Wales, Queensland, South Australia, Tasmania, Victoria and Western Australia formed one nation. They kept the systems of government that they had developed as separate colonies but also would have a federal government that was responsible for matters concerning the whole nation. When the Constitution of Australia came into force, the colonies collectively became states of the Commonwealth of Australia."  Answer:
The answer is:
Constitution