Bantu-speaking peoples who founded tribes during the Bantu expansions largely displaced and absorbed the earliest inhabitants of the region, the Pygmy people, about 1500 BC. The Bakongo, a Bantu ethnic group that also occupied parts of present-day Angola, Gabon, and the Democratic Republic of the Congo, formed the basis for ethnic affinities and rivalries among those countries. Several Bantu kingdoms—notably those of the Kongo, the Loango, and the Teke—built trade links leading into the Congo River basin.
The Portuguese explorer Diogo Cão reached the mouth of the Congo in 1484. Commercial relationships quickly grew between the inland Bantu kingdoms and European merchants who traded various commodities, manufactured goods, and people captured from the hinterlands. After centuries as a major hub for transatlantic trade, direct European colonization of the Congo river delta began in the late 19th century, subsequently eroding the power of the Bantu societies in the region.
French colonial era
The area north of the Congo River came under French sovereignty in 1880 as a result of Pierre de Brazza's treaty with King Makoko of the Bateke. This Congo Colony became known first as French Congo, then as Middle Congo in 1903. In 1908, France organized French Equatorial Africa (AEF), comprising Middle Congo, Gabon, Chad, and Oubangui-Chari (the modern Central African Republic). The French designated Brazzaville as the federal capital. Economic development during the first 50 years of colonial rule in Congo centered on natural-resource extraction. The methods were often brutal: construction of the Congo–Ocean Railroad following World War I has been estimated to have cost at least 14,000 lives.
During the Nazi occupation of France during World War II, Brazzaville functioned as the symbolic capital of Free France between 1940 and 1943. The Brazzaville Conference of 1944 heralded a period of major reform in French colonial policy. Congo benefited from the postwar expansion of colonial administrative and infrastructure spending as a result of its central geographic location within AEF and the federal capital at Brazzaville. It also received a local legislature after the adoption of the 1946 constitution that established the Fourth Republic.
Following the revision of the French constitution that established the Fifth Republic in 1958, the AEF dissolved into its constituent parts, each of which became an autonomous colony within the . During these reforms, Middle Congo became known as the Republic of the Congo in 1958 and published its first constitution in 1959. Antagonism between the Mbochis (who favored Jacques Opangault) and the Laris and Kongos (who favored Fulbert Youlou, the first black mayor elected in French Equatorial Africa) resulted in a series of riots in Brazzaville in February 1959, which the French Army subdued.
New elections took place in April 1959. By the time the Congo became independent in August 1960, Opangault, the former opponent of Youlou, agreed to serve under him. Youlou became the first President of the Republic of the Congo. Since the political tension was so high in Pointe-Noire, Youlou moved the capital to Brazzaville.
The Republic of the Congo received full independence from France on 15 August 1960. Youlou ruled as the country's first president until labour elements and rival political parties instigated a three-day uprising that ousted him. The Congolese military briefly took charge of the country, and installed a civilian provisional government headed by Alphonse Massamba-Débat.
Under the 1963 constitution, Massamba-Débat was elected President for a five-year term. During Massamba-Débat's term in office the regime adopted "scientific socialism" as the country's constitutional ideology. In 1965, Congo established relations with the Soviet Union, the People's Republic of China, North Korea and North Vietnam. Massamba-Débat's regime also invited several hundred Cuban army troops into the country to train his party's militia units and these troops helped his government survive a coup d'état in 1966 led by paratroopers loyal to future President Marien Ngouabi. Nevertheless, Massamba-Débat was unable to reconcile various institutional, tribal and ideological factions within the country and his regime ended abruptly with a bloodless coup in September 1968.
Ngouabi, who had participated in the coup, assumed the presidency on 31 December 1968. One year later, President Ngouabi proclaimed Congo Africa's first "people's republic", the People's Republic of the Congo, and announced the decision of the National Revolutionary Movement to change its name to the Congolese Labour Party (PCT). He survived an attempted coup in 1972 but was assassinated on 16 March 1977. An 11-member Military Committee of the Party (CMP) was then named to head an interim government, with Joachim Yhombi-Opango to serve as President of the Republic. Two years later, Yhombi-Opango was forced from power and Denis Sassou Nguesso become the new president.
Sassou Nguesso aligned the country with the Eastern Bloc and signed a twenty-year friendship pact with the Soviet Union. Over the years, Sassou had to rely more on political repression and less on patronage to maintain his dictatorship.
Pascal Lissouba, who became Congo's first elected president (1992–1997) during the period of multi-party democracy, attempted to implement economic reforms with IMF backing to liberalize the economy. In June 1996, the IMF approved a three-year SDR69.5m (US$100m) enhanced structural adjustment facility (ESAF) and was on the verge of announcing a renewed annual agreement when civil war broke out in Congo in mid-1997.
Congo's democratic progress was derailed in 1997, when Lissouba and Sassou started to fight for power in the civil war. As presidential elections scheduled for July 1997 approached, tensions between the Lissouba and Sassou camps mounted. On 5 June, President Lissouba's government forces surrounded Sassou's compound in Brazzaville and Sassou ordered members of his private militia (known as "Cobras") to resist. Thus began a four-month conflict that destroyed or damaged much of Brazzaville and caused tens of thousands of civilian deaths. In early October, the Angolan régime began an invasion of Congo to install Sassou in power. In mid-October, the Lissouba government fell. Soon thereafter, Sassou declared himself president.
A pro-constitutional reform rally in Brazzaville during October 2015. The constitution's controversial reforms were subsequently approved in a disputed election which saw demonstrations and violence.
In the controversial elections in 2002, Sassou won with almost 90% of the vote cast. His two main rivals, Lissouba and Bernard Kolelas, were prevented from competing and the only remaining credible rival, André Milongo, advised his supporters to boycott the elections and then withdrew from the race. A new constitution, agreed upon by referendum in January 2002, granted the president new powers, extended his term to seven years, and introduced a new bicameral assembly. International observers took issue with the organization of the presidential election and the constitutional referendum, both of which were reminiscent in their organization of Congo's era of the one-party state. Following the presidential elections, fighting restarted in the Pool region between government forces and rebels led by Pastor Ntumi; a peace treaty to end the conflict was signed in April 2003.
Sassou also won the following presidential election in July 2009. According to the Congolese Observatory of Human Rights, a non-governmental organization, the election was marked by "very low" turnout and "fraud and irregularities". In March 2015 Sassou announced that he wanted to run for yet another term in office and a constitutional referendum in October resulted in a changed constitution which allowed him to run during the 2016 presidential election. He won the election believed by many to be fraudulent. After violent protests in the capital, Sassou attacked the Pool region, where the Ninja rebels of the civil war used to be based, in what was believed to be a distraction. This led to a revival of the Ninja rebels who launched attacks against the army in April 2016, leading 80,000 people to flee their homes. A ceasefire deal was signed in December 2017.