How did Russia, Germany and Italy all became totalitarian dictatorships in the early 20th century?
Germany and Italy suffered through the economic chaos following World War I (especially in Germany), and the unrest and uncertainty in both cases led to the rise of two fascist dictators, Benito Mussolini and Adolf Hitler. The difference was that Mussolini took power much earlier, and made no pretense about his desire to rebuild the Roman Empire and run Italy as its strongman. As happened later in Germany with Hitler, Italians responded to the order and pride Mussolini brought to the country.
Adolf Hitler attempted a coup at around the same time Mussolini was coming to power, but failed and spent some time in prison. He then went the elective route and built a Nazi Party that, by 1930 was a major force at the polls. By 1932 his party controlled the Reichstag and the following year Hitler was appointed Chancellor. Soon after, he used a fabricated terror attack on the Reichstag building as an excuse to take dictatorial powers.
In the Soviet Union, a long civil war from 1917 - 1924 had painfully brought the Russia and its neighbors under communist control. When Soviet communism's founder Vladimir Lenin died in 1924, Josef Stalin rose to power by appointing his supporters to the Central Committee, the body that chose the leadership of the country. So Stalin was different from the previous two in that he took power in a system that was already largely dictatorial by nature.