Marx, like other socialists thinkers of the 10th century, denounced the cruel injustice of industrial capitalist society as he saw it. He had a vision of ending �the exploitation of man by man�and established a classless society, in wich all people would be equal. The only means to this end, he thought, was a revolution of the exploited (the proletariat) against the exploiters (the bourgeoisie), so that workers would on the means of production, such as the machines and the factories. This revolution would set up a �dictatorship of the proletariat� to do away with the old bourgeois order (the capitalist system) and eventually replaced it with a classless society.
Lenin took this idea and further focused on he role of the Communist Party as the leader of the working.
When Lenin reached Russia in 1917 a first revolution against the crumbling regime of the Czar had already taken place. The government was democratic, but the bourgeoisie. Lenin victoriously headed the radical socialist (Bolshevik) revolution in October of that year. This was immediately followed by four years of bloody civil war: the Revolution�s Red Army, organized and lead by Leon Trotsky, had to defend the �Whites� (Russian loyal to the Czar or just hostile to the communists) and foreign troops, too.
At Lenin�s death in 1924, there was a struggle between Joseph Stalin and trotsky for leadership of the Communist Party and thus of the nation. In 1925, Stalin clearly gained the upper hand; in 1927 he was able to expel Trotsky from the party. Later, Trotsky was exiled, then deported, and finally assassinated in Mexico, probably by a Stalinist agent, in 1940. All this time, Stalin never denounced Trorsky as a traitor.
Power in the Soviet Union became increasingly concentrated in Stalin�s hands. In the 1930's, massive arrests and a series of public trails not only eliminated all possible opposition, but loyal Bolshevik and hundreds of thousands of other absolutely innocent Russians.
still, people all over the world who felt the pull o Marx idea- an end to exploitation and oppression, as they saw it- thought of the Soviet Union as the country of the Revolution. It was hard for many people on the Left (who think of themselves as on the side of the exploited, and want major changes on society to attain social justice) to give up this loyalty.