The history of Russia begins with that of the East Slavs. The first East Slavic state, Kievan Rus', adopted Christianity from the Byzantine Empire in 988, beginning the synthesis of Byzantine and Slavic cultures that defined Russian culture for the next millennium. Kievan Rus' ultimately disintegrated as a state, finally succumbing to Mongol invaders in the 1230s. During this time a number of regional magnates, in particular Novgorod and Pskov, fought to inherit the cultural and political legacy of Kievan Rus'. After the 13th century, Moscow gradually came to dominate the former cultural center. By the 18th century, the Grand Duchy of Moscow had become the huge Russian Empire, stretching from Poland eastward to the Pacific Ocean. Expansion in the western direction sharpened Russia's awareness of its separation from much of the rest of Europe and shattered the isolation in which the initial stages of expansion had occurred. Successive regimes of the 19th century responded to such pressures with a combination of halfhearted reform and repression. Russian serfdom was abolished in 1861, but its abolition was achieved on terms unfavorable to the peasants and served to increase revolutionary pressures. Between the abolition of serfdom and the beginning of World War I in 1914, the Stolypin reforms, the constitution of 1906 and State Duma introduced notable changes to the economy and politics of Russia, but the tsars were still not willing to relinquish autocratic rule, or share their power. The Russian Revolution in 1917 was triggered by a combination of economic breakdown, war weariness, and discontent with the autocratic system of government, and it first brought a coalition of liberals and moderate socialists to power, but their failed policies led to seizure of power by the Communist Bolsheviks on October 25. Between 1922 and 1991, the history of Russia is essentially the history of the Soviet Union, effectively an ideologically based state which was roughly conterminous with the Russian Empire before the Treaty of Brest-Litovsk. The approach to the building of socialism, however, varied over different periods in Soviet history, from the mixed economy and diverse society and culture of the 1920s to the command economy and repressions of the Stalin era to the "era of stagnation" in the 1980s. From its first years, government in the Soviet Union was based on the one-party rule of the Communists, as the Bolsheviks called themselves, beginning in March 1918. However, by the late 1980s, with the weaknesses of its economic and political structures becoming acute, the Communist leaders embarked on major reforms, which led to the collapse of the Soviet Union. The history of the Russian Federation is brief, dating back only to the collapse of the Soviet Union in late 1991. Since gaining its independence, Russia was recognized as the legal successor to the Soviet Union on the international stage. However, Russia has lost its superpower status as it faced serious challenges in its efforts to forge a new post-Soviet political and economic system. Scrapping the socialist central planning and state ownership of property of the Soviet era, Russia attempted to build an economy with elements of market capitalism, with often painful results. Even today Russia shares many continuities of political culture and social structure with its tsarist and Soviet past.