Ukraine is a republic in eastern Europe which borders Russia to the east, Belarus to the north, Poland, Slovakia and Hungary to the west, Romania and Moldova to the southwest and the Black Sea to the south. The territory of present-day Ukraine was a key centre of East Slavic culture in the Middle Ages before being divided between a variety of powers, notably Russia, Poland, Lithuania and the Ottoman Empire. The area of today's Ukraine encompassed the formed the southern part of the first Eastern Slavic state, Kievan Rus'with its capital, Kiev, the capital of modern Ukraine. Kiev and Kievian Rus' were the seat of the Grand Prince of the Rurik Dynasty. The ruler of Kiev was also in effect the ruler of all the Rus' principalities. Kievan Rus' became weakened by internal quarrels and was destroyed by Mongol and Tatar invasions. On Ukrainian territory (Rus' in the narrow sense), the state of Kievan Rus' was succeeded by the principalities of Halych and Volodymyr-Volynskyi, which were merged into the state of Halych-Volynia. This was later subjugated by Lithuania and Poland, and after the 1376 marriage of Lithuania's Grand Duke Jagiello to Poland's Queen Jadwiga, was ruled by the Poles (see the Polish-Lithuanian Commonwealth). Although locally defeated, the Rurik Dynasty continued, first in Novgorod, and then in Moscow.
During the mid-17th century, a Cossack state, the Zaporozhian Host, was established by Ukrainians and others fleeing Polish serfdom. Located in central Ukraine, it was an autonomous military state, initially independent. Eastern Ukraine was eventually integrated into Russia as the Cossack Hetmanate, as a consequence of the controversial Treaty of Pereyaslav. After the partitions of Poland by Prussia, Austria and Russia at the end of the 18th century, Western Ukraine (Galicia) was taken over by Austria, while most of Ukraine was progressively assimilated into the Russian Empire. Ukrainians played an important role in continuous wars between East European monarchies and the Ottoman Empire.
Following the Russian Revolution in 1917, Ukraine was briefly independent in two states, then united, in 1920. By 1922 Ukraine was split between Poland and the Soviet Union. Also in 1922, most of Central and Eastern Ukraine became a constituent republic of the USSR as the Ukrainian SSR.
To satisfy the state's need for increased food supplies, the Soviet industrialization program called for the collectization of agriculture, which had a profound effect on Ukraine, the nation's breadbasket. In the late 1920s and early 1930s the state compounded the peasants' lands and animals into collective farms and state farms. Although the program was designed to affect all peasants, the plan met particularly heavy resistance from the wealthiest peasants, the kulaks, and a desperate struggle of the peasantry against the authorities ensued. Peasants slaughtered their cows and pigs rather than turn them over to the collective farms, especially in Ukraine, with the result that livestock resources remained below the 1929 level for years afterward. The state in turn forcibly collectivized reluctant peasants and deported kulaks and active rebels to Siberia. Within the collective farms, the authorities in many instances exacted such high levels of procurements that starvation was widespread. In some places, famine was allowed to run its course; and millions of peasants in Ukraine starved to death in a famine, called the Holodomor in Ukrainian.
During World War II, some elements of the Ukrainian nationalist underground fought both Nazi and Soviet forces, while others collaborated with the Nazis. In 1941 the German invaders and their Axis allies crushed the Red Army. In the encirclement battle of Kiev, the city was acclaimed by the Soviets as a "Hero City", for the fierce resistance of the Red Army and of the local population. More than 660,000 Soviet troops were taken captive.
After the Second World War, the borders of then-Soviet Ukraine were extended to the West (as stipulated in the Molotov-Ribbentrop Pac), uniting most Ukrainians under one political state. In 1954, Crimea was transferred from the RSFSR to Ukraine (Crimea has no continuous land bridge to the Russian Federation.) This decision of Nikita Khrushchev, intended to commemorate the 300th anniversary of the controversial Treaty of Pereyaslav, seen in Soviet historiography as the 'union of two fraternal peoples', led to tensions between Russia and Ukraine after the collapse of the Soviet Union.
Independence was achieved in 1991 with the collapse of the Soviet Union, and Ukraine was a founding member of the Commonwealth of Independent States. Despite the Soviet hegemony during most of the 20th century, Ukraine has been a member of the United Nations since the latter's inception in 1945.