Russia 1917: Countdown to Revolution

The names of Stalin, Lenin and Trotsky are infamous today. But in the space of a few mere months they went from obscure, slogan-shouting nobodies to supreme leaders of the largest nation on earth. The Russian Revolution was soaked in blood, both as it unfolded and during its tragic aftermath. How did these three lowly troublemakers change the world so dramatically in such a short space of time?