The region that is now modern-day Belarus was first settled by Slavic tribes in the 6th century. They gradually came into contact with the Varangians, a band of warriors consisting of Scandinavians and Slavs from the Baltics. Though defeated and briefly exiled by the local population, the Varangians were later asked to return and helped to form a polity—commonly referred to as the Kievan Rus'—in exchange for tribute. The Kievan Rus' state began in about 862 at the present-day city of Novgorod.
Upon the death of Kievan Rus' ruler, Prince Yaroslav the Wise, the state split into independent principalities. These Ruthenian principalities were badly affected by a Mongol invasion in the 13th century, and many were later incorporated into the Grand Duchy of Lithuania. Of the principalities held by the Duchy, nine were settled by ancestors of the Belarusian people. During this time, the Duchy was involved in several military campaigns, including fighting on the side of Poland against the Teutonic Knights at the Battle of Grunwald in 1410; the joint victory allowed the Duchy to control the northwestern border lands of Eastern Europe.
On February 2, 1386, the Grand Duchy of Lithuania and the Kingdom of Poland were joined in a personal union through a marriage of their rulers. This union set in motion the developments that eventually resulted in the formation of the Polish-Lithuanian Commonwealth, created in 1569. The Russians, led by Tsar Ivan the III, began military conquests in 1486 in an attempt to gain the Kievan Rus' lands, specifically Belarus and Ukraine. The union between Poland and Lithuania ended in 1795, and the commonwealth was partitioned by Imperial Russia, Prussia, and Austria, dividing Belarus. Belarusian territories were acquired by the Russian Empire during the reign of Catherine II and held until their occupation by Germany during World War I.
During the negotiations of the Treaty of Brest-Litovsk, Belarus first declared independence on 25 March 1918, forming the Belarusian People's Republic. The Germans supported the BPR, which lasted for about 10 months. Soon after the Germans were defeated, the BPR fell under the influence of the Bolsheviks and the Red Army and became the Byelorussian Soviet Socialist Republic in 1919. After Russian occupation of eastern and northern Lithuania, it was merged into the Lithuanian-Byelorussian Soviet Socialist Republic. Byelorussian lands were then split between Poland and the Soviets after the Polish-Soviet War ended in 1921, and the recreated Byelorussian SSR became a founding member of the Union of Soviet Socialist Republics in 1922.
In September 1939, as a result of the Molotov-Ribbentrop Pact, the Soviet Union invaded Poland and annexed its eastern lands, including most Polish-held Byelorussian land. Nazi Germany invaded the Soviet Union in 1941. Byelorussia was the hardest hit Soviet Republic in the war and remained in Nazi hands until 1944. During that time, Germany destroyed 209 out of 290 cities in the republic, 85% of the republic's industry, and more than one million buildings, while causing human losses estimated between two and three million (about a quarter to one-third of the total population). The Jewish population of Byelorussia was devastated during The Holocaust and never recovered. The population of Belarus did not regain its pre-war level until 1971. After the war ended, Byelorussia was among the 51 founding countries of the United Nations Charter in 1945 and began rebuilding the Soviet Republic. During this time, the Byelorussian SSR became a major center of manufacturing in the western region of the USSR, increasing jobs and bringing an influx of ethnic Russians into the republic. The borders of Byelorussian SSR and Poland were redrawn to a point known as the Curzon Line.
Joseph Stalin implemented a policy of Sovietization to isolate the Byelorussian SSR from Western influences. This policy involved sending Russians from various parts of the Soviet Union and placing them in key positions in the Byelorussian SSR government. The official use of the Belarusian language and other cultural aspects were limited by Moscow. After Stalin died in 1953, successor Nikita Khrushchev continued this program, stating, "The sooner we all start speaking Russian, the faster we shall build communism". When Soviet leader Mikhail Gorbachev began pushing through his reform plan, the Belarusian people delivered a petition to him in December 1986 explaining the loss of their culture. Earlier that year, Byelorussian SSR was exposed to nuclear fallout from the explosion at the Chernobyl power plant in neighboring Ukrainian SSR. In June 1988 at the rural site of Kurapaty near Minsk, archaeologist Zianon Pazniak, the leader of Christian Conservative Party of the BPF, discovered mass graves which contained about 250,000 bodies of victims executed in 1937-1941. Some nationalists contend that this discovery is proof that the Soviet government was trying to erase the Belarusian people, causing Belarusian nationalists to seek independence.
Two years later, in March 1990, elections for seats in the Supreme Soviet of the Byelorussian SSR took place. Though the pro-independence Belarusian Popular Front took only 10% of the seats, the populace was content with the selection of the delegates. Belarus declared itself sovereign on July 27, 1990, by issuing the Declaration of State Sovereignty of the Belarusian Soviet Socialist Republic. With the support of the Communist Party, the country's name was changed to the Republic of Belarus on August 25, 1991. Stanislav Shushkevich, the Chairman of the Supreme Soviet of Belarus, met with Boris Yeltsin of Russia and Leonid Kravchuk of Ukraine on December 8, 1991 in Belavezhskaya Pushcha to formally declare the dissolution of the Soviet Union and the formation of the Commonwealth of Independent States. A national constitution was adopted in March 1994, in which the functions of prime minister were given to the president.
Two-round elections for the presidency (24 June 1994 and 10 July 1994) resulted in the politically unknown Alexander Lukashenko winning more than 45 % of the vote in the first round and 80 % in the second round, beating Vyacheslav Kebich who got 14 %. Lukashenko was reelected in 2001 and in 2006.