The Commonwealth of Nations, normally referred to as the Commonwealth and formerly known as the British Commonwealth, is an intergovernmental organisation of fifty-three independent member states which grew out of the British Empire. Only two members, Mozambique and Rwanda, were not British colonies. The member states cooperate within a framework of common values and goals including the promotion of democracy, human rights, good governance, the rule of law, individual liberty, egalitarianism, free trade, multilateralism, and world peace. The Commonwealth is not a political union, but an intergovernmental organisation through which countries with diverse social, political, and economic backgrounds are regarded as equal in status.
The Commonwealth Secretariat is headed by the Secretary-General. Meetings of  Commonwealth Heads of Government are held every two years. Queen Elizabeth II is the Head of the Commonwealth and as such is a symbol of the members free association. Her Majesty is also the monarch of 16 members of the Commonwealth which are referred to as Commonwealth realms.Â
History
The first usage of the term ‘Commonwealth of Nations’ appears to be to have been in 1884 by Lord Rosebery when he was visiting Australia. He described the changing the British Eempire  with some of its colonies becoming more independent as a Commonwealth of Nations.Conferences of British and colonial prime ministers had occurred periodically since 1887, leading to the creation of the Imperial Conferences in 1911. The Commonwealth developed from the Imperial Conferences.
A specific proposal was presented by Jan Christian Smuts in 1917 when he coined the term “the British Commonwealth of Nations,” and envisioned the “future constitutional relations and readjustments in the British Empire.”  Smuts successfully argued that the Empire should be represented at the all-important Versailles Conference of 1919 by delegates from the dominions as well as Britain. In the Balfour Declaration at the 1926 Imperial Conference, Great Britain and its dominions agreed they were “equal in status, in no way subordinate one to another in any aspect of their domestic or external affairs, though united by common allegiance to the Crown, and freely associated as members of the British Commonwealth of Nations”. The members agreed that in future governors general should be appointed by the sovereign after consultation with and advice from the ministers of the respective Dominion.These aspects to the relationship were eventually formalised by the Statute of Westminster in 1931. Australia, New Zealand, and Newfoundland delayed ratification of the statute. Newfoundland never did as it joined Canada in 1948 . Australia and New Zealand did in 1942 and 1947 respectively.
British Commonwealth becomes The Commonwealth
After World War II, the British Empire was gradually dismantled to just 14 British overseas territories, still held by the United Kingdom today. In April 1949, following the London Declaration, the word “British” was dropped from the title of the Commonwealth to reflect its changing nature.  In addition, it was agreed that the overseas members should no longer be referred to as dominions, but rather as Commonwealth realms. Burma (also known as Myanmar, 1948), and Aden (1967) are the only states that were British colonies at the time of the war not to have joined the Commonwealth upon post-war independence.
Absent Friends
Among the former British colonies, protectorates and mandates which have  never become members of the Commonwealth are the United States (1776),  Egypt (independent in 1922), Iraq (1932), Transjordan (1946), British Palestine (part of which became the state of Israel in 1948), Sudan (1956), British Somaliland (which became part of Somalia in 1960), Kuwait (1961), Bahrain (1971), Oman (1971), Qatar (1971), and the United Arab Emirates (1971).
Republics
The issue of countries with constitutional structures not based on a shared Crown but that wanted to remain members of the Commonwealth, came to a head in 1948 with passage of the Republic of Ireland Act 1948, in which Ireland renounced the sovereignty of the Crown and thus left the Commonwealth. The Ireland Act 1949 passed by the Parliament of Westminster offered citizens of the Republic of Ireland a status similar to that of citizens of the Commonwealth in UK law.
In April 1949 at a Commonwealth prime ministers meeting in London, it was agreed that a realm could become a republic and if approved by the other members could remain within the Commonwealth. Under this London Declaration, India agreed that, when it became a republic, in January 1950, it would accept the British Sovereign as a “symbol of the free association of its independent member nations and as such the Head of the Commonwealth”.
Until 2007, Re-apply
Until 2007, a realm wishing to become a republic still had to reapply for membership of the Commonwealth. This would have to be approved by all members. In 1999, ACM revealed that Australian republicans, including the Attorney-General had overlooked the requirements of the London declaration. Constitutional monarchists criticised the Republicans for not ascertaing this and ensuring that there would be no objection from other members to any change of status. This would have required unanimous approval of other members. In practice approval seems to have been assumed in the absence of an objection. At that time Australia did not have the most friendly relations with the Malaysian Prime Minister, Dr Mahathir. He had vetoed our membership of another international group.
Now, change to a republic can be effected without reapplication provided the member is observing all of the Commonwealth criteria for membership. The judgement on this is made by the other members acting unanimously.  Thus it could be argued that the 2007 decision could still raise the issue of a veto following a change of status. Following India’s precedent, other nations became republics, or constitutional monarchies with their own monarchs, while some countries retained the same monarch as the United Kingdom, but their monarchies developed differently and soon became fully independent of the British monarchy. The monarch of each Commonwealth realm, whilst the same person, is regarded as a separate legal personality for each realm.