The United States of Africa is a concept of a federation of some or all of the 54 sovereign states and two disputed states on the continent of Africa. The concept takes its origin from Marcus Garvey's 1924 poem "Hail, United States of Africa". Kwame Nkrumah was the most prominent African political leader who passionately championed the idea of a Union of African States with a unified African Government, similar to the United States of America, as he envisioned an African government that could drive the continent forward.

The idea of a multinational unifying African state has been compared to various medieval African empires, including the Ethiopian Empire, the Ghana Empire, the Mali Empire, the Songhai Empire, the Benin Empire, the Kanem Empire and other historic nation states. During the late 19th and early 20th century the majority of African land was controlled by various European empires, with the British controlling around 30 percent of the African population at its peak.

The term "United States of Africa" was mentioned first by Marcus Garvey in his poem Hail, United States of Africa in 1924. Garvey's ideas and formation systems deeply influenced former Africa leaders and the rebirth of the African Union.

Between 1957 and 1966, Kwame Nkrumah, the first President of Ghana, was a strong advocate for the creation of a Union of African States with a Common African Government. Guided by Pan-African ideals, Nkrumah believed that for Africa to truly achieve independence and development, its nations needed to unite both politically and economically.

The All-African Peoples Conference, held in Accra, Ghana in 1958, marked a significant moment in the history of Pan-Africanism. Organized by Nkrumah and George Padmore, a Trinidadian writer and activist whom Nkrumah had appointed as his Advisor on African Affairs, the conference gathered representatives from across Africa and its diaspora and was the first time such an event had taken place on African soil, making it a pivotal occasion for Nkrumah to present his ambitious vision: the creation of a United States of Africa.

However, his proposal faced strong resistance from other African leaders, who feared losing their sovereignty, as well as from Western powers, who opposed it due to their own vested interests.

In February 2009, upon being elected chairman of the 53-nation African Union in Ethiopia, Muammar Gaddafi told the assembled African leaders: "I shall continue to insist that our sovereign countries work to achieve the United States of Africa." The BBC reported that Gaddafi had proposed "a single African military force, a single currency and a single passport for Africans to move freely around the continent". Other African leaders stated they would study the proposal's implications, and re-discuss it in May 2009.

The focus for developing the United States of Africa so far has been on building subdivisions of Africa - the proposed East African Federation can be seen as an example of this. Former President of Senegal, Abdoulaye Wade, had indicated that the United States of Africa could exist as early as 2017. The African Union, by contrast, has set itself the task of building a "united and integrated" Africa by 2025. Gaddafi had also indicated that the proposed federation may extend as far west as the Caribbean: Haiti, Jamaica, the Dominican Republic, the Bahamas and other islands featuring a large African diaspora, may be invited to join.