The Communists were able to centralize the Soviet government by the leadership of Vladimir I. Lenin, who took situations he could not control and turned them to his advantage. Lenin and to a greater extent Joseph Stalin firmly believed that revolution needed to be imposed on the people from above; they were incapable of a stable revolution by themselves.
At the time of the communist takeover, the Russian government was in a state of complete anarchy, simply waiting for a strong leader. Lenin provided that leadership. Lenin also possessed an unwavering determination to succeed which had not been present under the Czarist regime or the provisional government under Kerensky. On November 6,1917, a group headed by Leon Trotsky, Lenin's second in command, seized all government buildings and declared Lenin the head of a new government.
Lenin's speeches and promises appealed to the poor and to soldiers who were war weary. He promised land to the peasants (even though they had already rebelled and taken it from the landlords) and abandoned Russia's effort in World War I, accepting peace terms which were quite harsh. His charisma did a great deal to solidify leadership.
When his charisma and speeches were not enough, Lenin took further steps to tighten his control on power. He ordered Czar Nicholas II and his entire family shot so that there could be no pretenders to power. He also instituted a harsh police state. The Soviet secret state police, the Cheka, hunted down and executed thousands of people suspected of disloyalty or criticism of the government.
In the latter regard, the Soviet government was very similar to other communist governments. They cannot succeed by virtue of the will of the people alone; so they force government on them by means of terrorism and state police. Lenin himself once said "without terrorism there can be no revolution.