A Commonwealth realm is a sovereign state that has Charles III as its monarch and head of state. Charles succeeded his mother, Elizabeth II, as monarch of the Commonwealth realms immediately upon her death on 8 September 2022. All the realms are both equal with and independent of the others, though one person acts as monarch of each.
As of 2023[update], there are 15 Commonwealth realms: Antigua and Barbuda, Australia, The Bahamas, Belize, Canada, Grenada, Jamaica, New Zealand, Papua New Guinea, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, Solomon Islands, Tuvalu, and the United Kingdom. All are members of the Commonwealth of Nations, an intergovernmental organisation of 56 independent member states, 52 of which were formerly part of the British Empire. Charles III is also Head of the Commonwealth, a non-constitutional role.
The notion of these states sharing the same person as their monarch traces back to 1867 when Canada became the first dominion, a self-governing nation of the British Empire. With the growing independence of the dominions in the 1920s, the Balfour Declaration of 1926 originally established the Commonwealth of Nations, and that the nations were considered "equal in status ... though united by a common allegiance to the Crown". The Statute of Westminster 1931 further set the relationship between the realms and the Crown, including a convention that any alteration to the line of succession in any one country must be voluntarily approved by all the others. The modern Commonwealth of Nations was then formally constituted by the London Declaration in 1949 when India wanted to become a republic without leaving the Commonwealth; this left seven independent nations sharing the Crown: the United Kingdom, Canada, Australia, New Zealand, South Africa, Pakistan, and Ceylon (now Sri Lanka). Since then, new realms have been created through the independence of former colonies and dependencies, and some realms have also become republics. Barbados was the most recent realm to become a republic, doing so on 30 November 2021.