Pygmies are believed to be the original inhabitants of the region. They were largely displaced by Bantu groups that began spreading throughout the area about the first century A.D. Three Bantu kingdoms—the Kongo, Loango, and Teke—had become dominant by the time European explorers reached what is now the Congo in the late 15th century.

A Portuguese explorer, Diogo Cão, reached the Congo River in 1482 and set up trading posts along the Atlantic coast near its mouth. With the rise of the African slave trade in the 16th century, the French, British, and Dutch began to compete with the Portuguese and established more trading centers in the coastal area.

In the 1870's and 1880's Pierre Savorgnan de Brazza led a series of French expeditions into the interior. Under treaties that he signed with indigenous groups, territory on the north side of the Congo River became a French protectorate known as the French Congo. In 1885 the Congress of Berlin recognized French claims to the region. The name was later changed to Middle Congo. In 1910 it became part of French Equatorial Africa.

In 1958 Middle Congo achieved internal self-government as a member state of the newly established French Community and changed its name to Republic of Congo. It became fully independent on August 15, 1960, but remained in the Community.

In 1963 the elected government was forced to resign after a general strike and antigovernment demonstrations. It was succeeded by a socialist regime that took steps to nationalize the economy and to develop close ties with Communist nations. In 1968 a military tribunal assumed power. In 1970 the country's name was changed to People's Republic of the Congo, and a one-party political system based on Communism was established. The Congo withdrew from the French Community in 1973.

Violent demonstrations in 1990 forced the government to reorganize. Communism was abandoned and the country's name changed to Republic of the Congo. In 1992, a democratic constitution was adopted. Multiparty elections held for parliament and the presidency were won by opponents of the Communist regime. The long-time Communist ruler General Denis Sassou-Nguesso stepped aside after the elections but he retained support among segments of the military. With the assistance of troops from neighboring Angola, Sassou-Nguesso ousted the elected government in 1997, and reinstalled himself as president. Sporadic fighting continued between rebel groups and Sassou-Nguesso's forces.

A new constitution was adopted in 2002. Later that year, a presidential election was held, and Sassou-Nguesso won. In 2003, a peace deal ended a majority of the fighting, but a rebel group called the Ninjas did not immediately disarm.