In the eighteenth century, before all of the modern conveniences we know today, horses did a tremendous amount of manual labor. They were used to work farm fields, as transportation, and they hauled heavy coal from the mines. They were effective at their jobs, but just as all living creatures, they had their limitations. Weather conditions, hunger and thirst, sickness and fatigue were all factors that influenced a horse's performance.
James Watt, a Scottish engineer, invented a new steam engine that could do the work of the common horse and do it more efficiently and reliably.