de facto republic. New Zealand has made constitutional changes without difficulty in the past, such as the abolition of its upper house of parliament in 1951, the introduction of proportional representation in 1996 and most recently the creation of the Supreme Court of New Zealand as the court of final appeal. Legal academics have espoused the view that the legal changes required for a republic are not complex. Some have argued that the changes required are less radical than the move to MMP in 1996. Type of republic Most proponents of a republic, such as Sir Geoffrey Palmer and Andrew Butler, support a parliamentary republic, that is, a republic where the head of state and head of government are kept separate. Alison Quentin-Baxter and Janet McLean argue that republican advocates in New Zealand show "...a strong preference for constitutions based on the parliamentary system of government as being a more stable basis for democratic government than those based on a presidential system." A head of state in such a system would have the same reserve powers as the sovereign and governor-general. Treaty of Waitangi / Te Tiriti o Waitangi The Treaty of Waitangi () is an agreement signed between Māori tribes and representatives of the British Crown, signed in 1840. Because of the relationship between Māori and the Crown, the Treaty of Waitangi is often cited as a constitutional issue for a New Zealand republic. Some academics expressed concern that governments could use republicanism to evade treaty responsibilities. With the division of the Crown between the United Kingdom and New Zealand following the passing of the Statute of Westminster Adoption Act 1947, the "Crown in Right of New Zealand" became party to the Treaty. Legal academics state that the Treaty would be unaffected by New Zealand becoming a republic, as the new head of state would inherit the Crown's responsibilities. In 2004, Professor Noel Cox argued "In strict legal terms, if New Zealand became a republic tomorrow it would make no difference to the Treaty of Waitangi. Speaking as a lawyer, it's a long-established principle that successive governments take on responsibility for previous agreements." Realm of New Zealand The Realm of New Zealand consists of New Zealand proper and two states in free association, Niue and the Cook Islands. Should New Zealand become a republic, the Realm of New Zealand would continue to exist without New Zealand, the Ross Dependency