The Constitutional history of Australia is the history of Australia's foundational legal principles. Australia's legal origins as a nation state began in the colonial era, with its legal system reliant initially upon a legal fiction of terra nullius to impose British law upon the colony of New South Wales. As the colonies expanded, Australia gradually began to achieve de facto independence. Over the years as a result the foundations of the Australian legal system gradually began to shift. This culminated in the Australia Act, an act formally ending legal ties with the UK.