A little history of the sport
Competitive motocross got its start in 1924, with the first-ever Scrambles being held in Surrey in the UK. Over the ensuing decades, the sport would evolve mostly due to the European riders who modified the racing surface, adding length and obstacles. Motocross became popular in the 1930s, especially in the UK, where district-wide events were regularly held. The motorcycles used at the time were, for the most part, indistinguishable from bikes ridden on the street.
Through the 1950s to the 1970s, competition and difficulty of terrain increased. The technology utilized in designing bikes for competition vastly improved; the biggest breakthrough of this time period was arguably the moving "swing arm" suspension. It was invented during the earliest part of the 1950s. The governing body for international motorcycle racing held the European Championship for 500cc machines in 1952; this series was changed to the World Championships in 1957. In 1962, a 250cc series was added as two-stroke bikes were becoming more competitive.
European companies began to build motorcycles that were prized for their maneuverability and light weight. Improvements in technology in the 1960s meant that older, heavier four-stroke bikes began to be used only in smaller events. At the end of the 1960s, Japanese companies began to compete in earnest with their European counterparts. In 1970, Suzuki became the first Japanese company to win a championship (the 250cc series). In 1975, the 125cc World Championships were introduced, and motocross became more popular in the US. Europeans continued to be competitive, but American riders improved greatly and began to win races.
During the 1980s, further technological advances were brought about by the innovative nature of Japanese motorcycle companies. The biggest improvements of this time period were the radiator and the monoshock suspension. In the 1990s, laws were enacted to force motorcycle manufacturers to abide by more environmentally-friendly rules. More recently, new motocross disciplines have become popular. Arena races, supercross and freestyle motocross draw thousands of spectators to see high jumps and unbelievable stunts.