The term Unilateral Declaration of Independence (UDI) was used when Rhodesia became Zimbabwe and declared independence in 1965 from the United Kingdom (UK) without an agreement with the UK.
Previously published on 15 October 2014, Updated 1 July 2016
A Unilateral Declaration of Independence (UDI) is a formal process leading to the establishment of a fully recognized state, which declares itself an independent and sovereign pre-existing state without a formal agreement with the occupying nation state, because the two have never been together.
The current move by the Commonwealth government's Recognise campaign to include Aboriginal people in the Australian Constitution (which is a 1900 Act of the British Parliament) clarifies that Aboriginal Nations and Peoples are NOT in the Australian Constitution and are therefore outside it and continue to be independent. Unilateral Declarations of Independence are not a radical action in any way, but are stating what the current situation is.
Under international law every Nation has the right to govern itself the way it chooses to in its culturally appropriate way. Every Nation has to have a land base, a population, law, and the ability to enter into international relations. It is well documented that Aboriginal Nations and Peoples traded with each other along the songlines and trading routes, as well as trading overseas into countries now known as Papua Nuigini, West Papua, Indonesia, Maluku, Malayasia and China.
When decolonization was in full swing in Africa and other areas Australia was left out of the process by what was called the "Blue Water Principle".
The term Unilateral Declaration of Independence was used when Rhodesia became Zimbabwe and declared independence in 1965 from the United Kingdom (UK) without an agreement with the UK. 
Prominent examples of unilateral declarations of independence include that of the United States in 1776, [Don H. Doyle. Secession as an International Phenomenon: From America's Civil War to Contemporary Separatist Movements. University of Georgia Press, 2010] the Irish Declaration of Independence of 1919 by a revolutionary parliament, the attempted secession of Biafra from Nigeria in 1967, the Bangladeshi declaration of independence from Pakistan in 1970, the (internationally unrecognized) secession of the Turkish Republic of Northern Cyprus from Cyprus in 1983, the Palestinian Declaration of Independence of the Palestinian territories in 1988, and that of the Republic of Kosovo in 2008 which was suffering a humanitarian crisis. 
During the breakup of Yugoslavia, the government of the United States asked the governments of Slovenia and Croatia to drop their UDI plans because of the threat of major war erupting in the Balkans because of it, and the USA threatened that it would oppose both countries' UDIs on the basis of the Helsinki Final Act if they did so. However, four days later both Slovenia and Croatia announced their UDIs from Yugoslavia. 
The High Court of Australia in Mabo (No. 2) 1992 confirmed that Aboriginal Peoples continue to hold title to Country by way of pre-existing and continuing Law, Culture and custom. The High Court also confirmed that Aboriginal Law, Culture and customs come from the Peoples and the land and we are governed according to these Laws that were existing before the British invasion, misleadingly called 'settlement'. This makes Aboriginal Law, Culture and custom the Law of the Land, the continental common law, which continues to this day. But, thanks to agreement from the 'Magnificent Seven', the 1993 Native Title Act as amended, is a fraudulent attempt by the federated colonial government of Australia to steal all these rights by statute.
In the international legal context, however, the continental common law of the land can never be legislated away from the people, unless the people themselves negotiate to do so with their full free prior and informed consent to the terms they settle on. No other way is possible. For a colonial power to do otherwise is an act of war against the Nations and Peoples of the land, and then we are governed by a Police State under Martial Law.
In the 1980s a Treaty campaign resulted in the former PM Malcolm Fraser accepting, on behalf of all Australians, that the pre-existing Aboriginal sovereign nations had not ceded sovereignty to the British and also accepted as a second precondition to the negotiation of a treaty that Aboriginal people had pre-existing, continuing proprietary rights in the lands known as Australia and its waters.
Despite PM Fraser and the National Aboriginal Conference (NAC) reaching agreements on the underpinning preconditions, the Attorney-General at the time advised the PM Fraser and the Department of Aboriginal Affairs that to use the term 'Treaty' was to signify an agreement between internationally recognised States and it was this reality that the Fraser government was advised to avoid at all costs. Instead it was recommended that a compact or a domestic agreement such as a Makarrata (the Aboriginal choice of words at the time) be entered into. This was essentially domesticating the Aboriginal resistance and movement. The legal advice to Fraser went onto say that the Commonwealth should be careful to avoid falling in to a trap of recognizing individual Aboriginal Nations under Australian domestic law where Aboriginal Nation States be recognized independent domestic sovereign states along the same lines as the Native Americans. [ http://nationalunitygovernment.org/content/word-treaty ]
In the American case as it stands today many native Indian tribes have some vast territories where they govern independently of local States such as in North and South Dakota, where, on and within these territories, native Indian laws apply and no State law or federal laws can interfere with the way they choose to govern themselves. They control their own economy, their own education system and they conduct their own ceremonial practices. They still have conflict, however, over resources and resource development, but they have won significant court cases in recent times regarding past wrongful acts by governments and have won significant compensation.
Their world is not iron clad secure, because they can be subject to laws being changed in relation to their treaty arrangements by way of Congress and Presidential decrees. Recent legal history shows that any Act to alter the laws which impact on their rights is so often meet with massive compensation pay outs.
On the other hand, the Commonwealth of Australia case demonstrates that its objective is for some of the assimilated educated Aboriginal people to work on deceitful national projects to:
The governmental regime across Australia is now currently committing a major international crime against our people by conducting a similar action that is being perpetrated throughout the middle east by the Islamic state, IS, by amending heritage legislation throughout Australia, and thereby give rights to mining companies and others under and within the Australian legal system to destroy our ancient religious sites, ceremony grounds, sacred places and to collect our material cultural objects and to put them in boxes locked away in keeping places and museums under their control thereby totally destroying our physical cultural existence from the face of Australia. This is aimed at the deliberate desecration of all things Aboriginal in the environment and on the landscape, which results in ensuring that Aboriginal people have no past, no record throughout the millennia, and our past becomes a distant memory. If we become people with no past, then we will have no future as Aboriginal Peoples, thus becoming spiritually sterilized Australians.
We who took up the mantle of our Old People in their fight for civil rights and our Aboriginal identity have a moral obligation to stay the course, fight the fight and locate solutions. In the words of Mahatma Ghandi: "First they ignore you, then they laugh at you, then they fight you, then you win."