The Twa were the original inhabitants of Rwanda and were followed (c.A.D. 1000), and then outnumbered, by the Hutus. In the 14th or 15th cent., the Tutsis migrated into the area, gained dominance over the Hutus, and established several states. By the late 18th cent. a single Tutsi-ruled state occupied most of present-day Rwanda. It was headed by a mwami (king), who controlled regionally based vassals who were also Tutsi. They in turn dominated the Hutus, who, then as now, made up the vast majority of the population. Rwanda reached the height of its power under Mutara II (reigned early 19th cent.) and Kigeri IV (reigned 1853–95). Kigeri established a standing army, equipped with guns purchased from traders from the E African coast, and prohibited most foreigners from entering his kingdom.

Nonetheless, in 1890, Rwanda accepted German overrule without resistance and became part of German East Africa. A German administrative officer was assigned to Rwanda only in 1907, however, and the Germans had virtually no influence over the affairs of the country and initiated no economic development. During World War I, Belgian forces occupied (1916) Rwanda, and in 1919 it became part of the Belgian League of Nations mandate of Ruanda-Urundi (which in 1946 became a UN trust territory). Until the last years of Belgian rule the traditional social structure of Rwanda was not altered; considerable Christian missionary work, however, was undertaken.

In 1957 the Hutus issued a manifesto calling for a change in Rwanda's power structure that would give them a voice in the country's affairs commensurate with their numbers, and Hutu political parties were formed. In 1959, Mutara III died and was succeeded by Kigeri V. The Hutus contended that the new mwami had not been properly chosen, and fighting broke out between the Hutus and the Tutsis (who were aided by the Twa). The Hutus emerged victorious, and some 100,000 Tutsis, including Kigeri V, fled to neighboring countries. Hutu political parties won the election of 1960; Grégoire Kayibanda became interim prime minister. In early 1961 a republic was proclaimed, which was confirmed in a UN-supervised referendum later in the year. Belgium granted independence to Rwanda on July 1, 1962.

Kayibanda was elected as the first president under the constitution adopted in 1962 and was reelected in 1965 and 1969. In 1964, following an incursion from Burundi, which continued to be controlled by its Tutsi aristocracy, many Tutsis were killed in Rwanda, and numerous others left the country. In 1971–72, relations with Uganda were bitter after President Idi Amin of Uganda accused Rwanda of aiding groups trying to overthrow him. In early 1973 there was renewed fighting between Hutu and Tutsi groups, and some 600 Tutsis fled to Uganda.

On July 5, 1973, a military group toppled Kayibanda without violence and installed Maj. Gen. Juvénal Habyarimana, a moderate Hutu who was commander of the national guard. In 1978 a new constitution was ratified and Habyarimana was elected president. He was reelected in 1983 and 1988. In 1988 over 50,000 refugees fled into Rwanda from Burundi.

Two years later Rwanda was invaded from Uganda by forces of the Rwandan Patriotic Front (RPF), consisting mainly of Tutsi refugees. They were repulsed, but Habyarimana agreed to a new multiparty constitution, promulgated in 1991. In early 1993, after Habyarimana signed a power-sharing agreement, Hutu violence broke out in the capital; subsequently, RPF forces launched a major offensive, making substantial inroads. A new accord was signed in August, and a UN peacekeeping mission was established. However, when Habyarimana and Burundi's president were killed in a suspicious plane crash in Apr., 1994, civil strife erupted on a massive scale. Rwandan soldiers and Hutu gangs slaughtered an estimated 500,000–1 million people, mostly Tutsis and moderate Hutus. The RPF resumed fighting and won control of the country, but over 2 million Rwandans, nearly all Hutus, fled the country.

In a gesture of reconciliation, the RPF named Pasteur Bizimungu, a Hutu, as president, but there were reprisals against Hutus by elements of the Tutsi-dominated army, and real power was believed to lie with RPF leader Paul Kagame, who became vice president and defense minister. The Hutu refugees remained crowded into camps in the Congo (then called Zaïre) and other neighboring countries, where Hutu extremists held power and, despite relief efforts by the United Nations and other international organizations, disease claimed some 100,000 lives. In 1995, a UN-appointed tribunal, based in Tanzania, began indicting and trying a number of higher-ranking people for genocide in the Hutu-Tutsi atrocities; however, the whereabouts of many suspects were unknown, and by 2003 only 17 people had been convicted and sentenced. Many individuals were also tried in Rwandan courts, but by 2002 slightly less than 5,000 (of 120,000 charged with crimes) had been tried. Over a million Hutu refugees flooded back into the country in 1996; by 1997, there was a growing war between the Rwandan army and Hutu guerrilla bands.

In 1998, Rwandan soldiers began aiding antigovernment rebels in the Congo who were attempting to overthrow the Congolese president, Laurent Kabila; Rwanda had helped Kabila overthrow Mobutu Sese Seko 18 months earlier. President Bizimungu resigned in Mar., 2000, accusing the parliament of using an anticorruption campaign to attack Hutu members of the government. Kagame officially succeeded Bizimungu as president in April, becoming the first Tutsi to be president of Rwanda.

Fighting in 1999 and 2000 between Rwandan and Ugandan forces in the Congo has led to tense relations between the two nations and occasional fighting between proxy forces in the Congo; each nation also has accused the other of aiding rebels against its own rule. Rwandan troops were withdrawn from the Congo in 2002 as the result of the signing of a peace agreement, but Rwanda forces fighting Hutu rebels have made incursions into the Congo and Burundi as well. Also in 2002, former president Bizimungu, who had become a critic of the government and established an opposition party, was arrested and charged with engaging in illegal political activity; he was convicted in 2004, but released in 2007 after being pardoned.

In May, 2003, votes approved a new constitution. In the subsequent presidential election in July, President Paul Kagame faced three Hutu candidates, the most prominent of which was former prime minister Faustin Twagiramungu. The election, the first in which Rwandans could vote for an opposition candidate, was won by Kagame, with 95% of the vote, but some observers accused the government of voting irregularities, and the campaign was marred by continual government interference with opposition rallies. The RPF also won a majority of the elected seats in the Chamber of Deputies in September. The main Hutu rebel group, based in E Congo (Kinshasa), announced in Mar., 2005, that it would disarm and return peacefully to Rwanda, but the Rwandan government said that rebels who participated in the 1994 genocide would face trial when they returned.

In late 2006, a French judge investigating the crash that killed Habyarimana and provoked the genocide concluded that Kagame and a number of his aides should be tried for their roles in shooting down the plane; the judge was investigating the crash because of the deaths of the plane's French crew. The Rwandan government, which had accused extremist Hutus of assassinating Habyarimana and which also was investigating what it said was French complicity in the massacres that followed the crash, angrily denounced the judge's action and expelled the French ambassador. Ties between the two nations were reestablished only in early 2008.