This form of racing has experienced high levels of popularity over the years, particularly in the post-World War II time frame. The "golden era" of the 1950s was followed by a decade of transition and innovation in the 1960s, which included increased international participation. The sport experienced considerable growth and exposure during the rising popularity of the CART PPG Indy Car World Series in the 1980s and early 1990s. Two organizational disputes, in 1979 and 1996, led to a "split" that divided the participants (and fans) among two separate sanctioning bodies. However, an official unification took place in 2008 that brought the sport back together under one single sanctioning body.