It is said that around the 1860s when farming machines were pulled by horse, farmers would boast about the strength of their horses. They would claim that their horse could tow large loads, such as a fully loaded hay cart or wagon. Farmers would challenge one another to contests to prove who had the strongest horse. A barn door was removed and laid flat on the ground, and the horse was then hitched to it, the farmer would then urge the horse to drag the barn door along the ground. One by one, people jumped on the door until the horse could no longer drag it; the horse pulling the most people the greatest distance was judged the strongest. This event, called horse pulling, is still carried out today with specially bred horses trained to have high strength and low stamina, rather than low strength and high stamina which is normally the case with racing horses. Instead of people, fixed weights on sleds are dragged as far as possible. While it is said that the term horsepower is derived from this event, in reality the term was coined by James Watt. It wasn’t until 1929 that motorized vehicles were put to use in the first events at Vaughansville, Missouri and Bowling Green, Ohio[citation needed], the latter being where the current national championships are held. Although the sport was recognized then, it did not really become popular until the 50s and 60s. It was also realized, at that time, there were no uniform set of rules. The rules varied from state to state, county to county, and competitors never knew what standards to follow. This made the sport difficult for new entrants. SOURCE: wIkipedia.org