Thoroughbred racing has always been the "Sport of Kings," but harness racing was the "Everyman's Sport." Thoroughbreds were for wealthy businessmen and sheikhs, but everyone knew
someone with a Standardbred. For all the grace and class of Thoroughbreds, they didn't get much faster. Harness racing was exciting because every year, the records would get lower and lower, and going to the track meant you might see history made. At one point there were more harness racing fans than baseball fans in the US. Popular songs like "Camptown Races," "Jingle Bells," and "Old Gray Mare" were all written about Standardbreds. But with the development of the car, Standardbreds and other working horses became less and less prevalent, and it wasn't until after the Great Depression in the 1930s that harness racing began to pick up speed again -- literally.
*All credit for the information goes to http://www.nowthatsatrot.blogspot.com/, I found all the pictures on http://www.google.com/*
For more information, check out the USTA's website at http://www.ustrotting.com/