The engine that converts heat into mechanical work by using steam pressure — the foundational technology of the Industrial Revolution, which for the first time gave humanity a practical way to convert stored energy (coal) into unlimited mechanical power, breaking the constraint that had bound all previous economies to the limits of human and animal muscle.
Before the steam engine, all the work in the world was done by muscles — human or animal — or by wind and water, which are themselves products of solar energy. The total work available was limited. You could have more workers or more oxen or better waterwheels, but the ceiling was determined by biological and geographic constraints. The steam engine broke this ceiling. For the first time, stored energy — coal laid down over millions of years — could be converted into mechanical work without limit. The implications took decades to unfold. But the steam engine's first successful application was not the famous industrial uses. It was pumping water out of coal mines, to get more coal to power more steam engines. The feedback loop was there from the beginning.