The Christians effectively toppled (or consumed from within) the Roman empire, starting from an exceptionally small base.
Starting from a small group in each country, Communists took over Russia and China - the world's largest countries by land mass and population - and they did it exceptionally quickly considering.
Other examples: Simon Bolivar, Fidel Castro, the Founding Fathers, Khmer Rouge, Saddam Hussein, 1979 Iranian revolution, the Taliban. And those are just a few examples from the last couple hundred years. History is littered with a gazillion more, small and large, of varying ideologies. None of which needed smart phones or the Internet.
These types of things have always happened throughout history.