Steam power is one of the first methods developed for powering machines, and sparked the Industrial Revolution. It was developed early, because precision machining and tight-fitting pistons are not required for building effective steam engines.
Steam has been superseded by electricity and internal combustion engines for some classes of machines, but remains important in others. Large stationery power plants, such as those used to drive generators in electric power plants, are often steam-driven, and, in fact in most nuclear power plants, the nuclear reactor boil water into superheated steam, which in turn drives the steam turbines which drive the generators.