The Commonwealth is a free association of independent states under the British monarch, while the British Empire, the largest in history, was composed of dominions, colonies, mandates, and other territories acquired since the 16th century.

For more than a century, the empire was hailed as the foremost global power. At its peak in 1921, the British ruled a population of 570 million people, covering more than 14 million square miles—a quarter of Earth’s total land area.

The late queen came to the throne in 1952, just before what history recalls as a period of rapid decolonization in the 1960s.

Britain was very much still in possession of more than 70 overseas territories, but even as Elizabeth started her reign, it was clear that the empire was not to last.

India, once called “the jewel in the crown” of the British Empire, had won independence just five years before Elizabeth became queen. In 1952, British troops were fighting uprisings in Egypt and Kenya, with both countries later winning their independence.

As years passed, the empire continued to shrink until Hong Kong was transferred to China in 1997. The queen’s son—now King Charles III—dubbed it the “end of the empire.”

The British Empire has been criticized for its contribution to slavery, particularly in the sugar-producing islands of the Caribbean and the movement of African people for profit. It is estimated that 12 million Africans were captured and transported into slavery, with at least one-third of these carried in British ships.

Throughout the 18th and 19th centuries, the huge sugar plantations across the Caribbean provided around 80 percent of the sugar consumed in Western Europe. Relying on slavery to complete the labor-intensive work, this market helped make Britain the prosperous superpower it became.

Long before the reign of Queen Elizabeth II, the 1833 Slavery Abolition Act was introduced to abolish slavery in most British colonies, freeing thousands of enslaved Africans in the Caribbean and South Africa.

The modern Commonwealth emerged from the British Commonwealth of Nations created by the Balfour Declaration of 1926.

Before the empire was disbanded, the modern Commonwealth was founded in 1949, when eight countries came together as “free and equal members of the Commonwealth of Nations, freely co-operative in the pursuit of peace, liberty and progress.”

While the legacy of the empire and its history remains, the modern Commonwealth represents a progression in the British royal family’s role in the world.

On her 21st birthday in 1947, then Princess Elizabeth was with her parents on a tour of South Africa where she gave a speech broadcast from Cape Town and dedicated her life to the service of the Commonwealth. She would become its head on the death of her father, King George VI, in 1952.

During that speech, Queen Elizabeth said: “I declare before you all that my whole life, whether it be long or short, shall be devoted to your service and the service of our great imperial family to which we all belong.”

Today, the British monarch King Charles III remains the ruler of 15 of the 56 Commonwealth nations, which include the U.K and India.

The 15 nations the king rules are: Antigua and Barbuda, Australia, The Bahamas, Belize, Canada, Grenada, Jamaica, New Zealand, Papua New Guinea, St. Kitts and Nevis, St. Lucia, and Tuvalu. These countries contain around 2.2 billion people. Thirty-six other members are republics, and five others have different monarchs.

Passionate about supporting her subjects throughout the Commonwealth, in 2014 Queen Elizabeth II launched The Queen’s Young Leader Award, recognizing and celebrating exceptional people aged 18 to 29 from across the Commonwealth.

She said: “The Commonwealth can only flourish if its ideas and ideals continue to be young and fresh and relevant to all generations.”

Earlier this year, King Charles III gave an opening address at a Commonwealth heads of government meeting in Rwanda and called on member states to acknowledge the wrongs that have shaped our past" and said the “time has come” for conversations about historic slavery.

As the Commonwealth nations join the British people in mourning their queen, mixed feelings from former colonies of the empire and questions about the future of the monarchy’s role remain.