Revolution: A forceable overthrow of an existing government or social order, in favor of a new system.
Bolshevik: A member of the Russian Social Democrat Party. Later renamed the Communist Party.
Democratic Centralism: The organizational principles of Communist parties. For example, all directors of the Party shall be elected, top to bottom, and then supported fully by the losers; the minority subordinated to the majority.
There was an attempt at revolution in Russia in 1905, after their disastrous war with Japan, but the Tsar was able to put down that attempt. Sort of. Not all the unrest was directed at the government; there was widespread dissatisfaction with the average Russian's lot in life in general. There were strikes and terrorist attacks and military mutinies and so on. The Tsar had to compromise in order to remain in power, and was forced to allow that most hated of institutions (to a monarch): a parliament. In Russian, a parliament is called a Duma.
Unrest settled down a bit, and by 1913 when the Tsar celebrated his family's 300th year in power, the crowds turned out. When World War I started the following year, the Russian people rallied as one and the Tsar had never really known such popularity as he stood before the chapel altar in the Winter Palace and spoke the vow never to conclude peace as long as a single enemy remained on Russian soil. It was the same words his great-great-grandfather, Alexander I, spoke in 1812 when Napoleon Bonaparte invaded Russia. Alexander was, at least, able to keep his word, pursuing the French all the way back to Paris after the Russian winter killed Napoleon's army. They left behind the word "bistro" which is the French version of a Russian word meaning "hurry up" or "make it snappy."
Tsar Nicholas, however, would not be involved when peace was concluded this time.
A recently hopeful revolutionary by the name of Vladimir Lenin was about as dejected as a would-be revolutionary could be. He must have thought revolution would never come to pass after all. He had lived in exile since 1907, and he continued his frustrated existence in his sparse walk-up flat in Switzerland with his butt-ugly wife Nadezhda Krupskaya.
Fame and good fortune and adoration are all fleeting, of course. The war went badly for the Russians and the unwashed smell of revolution again filled the frosty air in early 1917. The Tsar abdicated and he and his family were placed under house arrest by the provisional government of Alexander Kerensky. That was in March (O.S.) Kerensky decided to fight on against the Germans, who retaliated by sending a frothing-at-the-mouth Lenin back to Russia in a sealed boxcar like some sort of smallpox bacillus. Which he was, of course.
Enter the second Russian Revolution of 1917, the October Revolution of Lenin and his Bolsheviks. Goodbye Tsar and family. Goodbye Russia. Hello Communism.
The word "Bolsheviks" actually just means "majority," which they were (politically speaking) compared to the Mensheviks in 1905. They kept the name after the revolution until, in about 1952, it occurred to papa Stalin that they were no longer a "majority" any more — they were an "only" now. Then they changed to just plain Communists.
Although it is possible to click on this image and enlarge it, I wish you wouldn't.