The championship was an international series established by the American Motorcyclist Association as a pilot event to help establish motocross in the United States.
The races run on American tracks to international standards, featuring the top riders from the F.I.M.
In 1970 and 1971, the highest placing American rider at the end of the series was considered the A.M.A.
[1] Since riders were paid based upon their results rather than starting money paid in European races, fewer European riders were motivated to make the costly trans-atlantic voyage.
[1] The Inter-AMA series was a similar year-end championship, but used a 250cc engine displacement formula.