Companies such as Husqvarna from Sweden, CZ from the former Czechoslovakia and Greeves from England, became popular due to their lightness and agility.[4] By the 1960s, advancements in two-stroke engine technology meant that the heavier, four-stroke machines were relegated to niche competitions.[4] Riders from Belgium and Sweden began to dominate the sport during this period.[2] Motocross was introduced to the United States in 1966 when Swedish champion, Torsten Hallman rode an exhibition event against the top American TT riders at the Corriganville Movie Ranch also known as Hopetown in Simi Valley, California. The following year Hallman was joined by other motocross stars including Roger DeCoster, Joël Robert, and Dave Bickers. They dominated the event placing their lightweight two-strokes into the top six finishing positions.[5][6] Motocross began to grow in popularity in the United States during this period, which fueled an explosive growth in the sport.[7]