In precolonial times, the region now called the Republic of Congo was dominated by three kingdoms: Kongo (originating about 1000), the Loango (flourishing in the 17th century), and Tio. After the Portuguese located the Congo River in 1482, commerce was carried on with the tribes, especially the slave trade.

The Frenchman Pierre Savorgnan de Brazza signed a treaty with Makoko, ruler of the Bateke people, in 1880, thus establishing French control. It was first called French Congo, and after 1905 Middle Congo. With Gabon and Ubangi-Shari, it became the colony of French Equatorial Africa in 1910. Abuse of laborers led to public outcry against the French colonialists as well as rebellions among the Congolese, but the exploitation of the native workers continued until 1930. During World War II the colony joined Chad in supporting the Free French cause against the Vichy government. The Congo proclaimed its independence without leaving the French Community in 1960, calling itself the Republic of Congo.

The Congo's second president, Alphonse Massemba-Débat, instituted a Marxist-Leninist government. In 1968, Maj. Marien Ngouabi overthrew him but kept the Congo on a Socialist course. He was sworn in for a second five-year term in 1975. A four-man commando squad assassinated Ngouabi on March 18, 1977. Col. Joachim Yhombi-Opango, army chief of staff, assumed the presidency on April 4. Yhombi-Opango resigned on Feb. 4, 1979, and was replaced by Col. Denis Sassou-Nguesso.

In July 1990 the leaders of the ruling party voted to end the one-party system. A national political conference, hailed as a model for sub-Saharan Africa, renounced Marxism in 1991 and scheduled the country's first free elections for 1992. Pascal Lissouba became the country's first democratically elected president.

Political and ethnic tensions intensified in 1993 after legislative elections, when the opposition's rejection of the results developed into violence. A peace agreement was signed between the government and the opposition in Aug. 1994. A four-month civil war (June 5–Oct. 15, 1997) devastated Brazzaville, the capital. Buttressed by military aid from Angola, former Marxist dictator Denis Sassou-Nguesso overthrew President Lissouba. In late 1999 a peace agreement was signed between Sassou-Nguesso, who comes from the north, and the rebels representing the populous south. The postwar period has been traumatic for the desperately poor country.

In March 2002, President Sassou-Nguesso was reelected with 89.4% of the vote. His opponents were either barred from the country or withdrew from the election.

The so-called Ninja rebels continued to battle government forces, each attempting to gain or maintain control of the country's rich oil reserves and each seemingly unconcerned about the toll this new outbreak of violence took on civilians. In May 2003, the government and Ninja rebels signed an agreement to end hostilities.