Since you asked, I will quote wikipedia on this issue:
Cannabis was criminalized across most of the world in the early parts of the 20th century. The reasons for and approaches to criminalization vary from country to country, but the most substantial factor in global terms has been the influence of the drug policies of successive United States federal administrations, as embodied in the U.S. Federal Bureau of Narcotics, founded in 1930, and its successor, the U.S. Drug Enforcement Administration, formed in 1973. Through these and other agencies, the U.S. government energetically lobbied both nationally and internationally from 1930 onwards for the criminalization of cannabis and its use, and the campaign was largely successful.
http://en.wikipedia.org/wiki/Legal_issues_of_cannabis#Criminalization
So yeah, I guess it is our fault.
Don't get me wrong, I'm not a pothead or anything, but I hate the idea of people spending their entire lives in jail over it because it's totally fucking harmless. To take someone's life from them because they were in possession of some herb is arbitrary and totally fucked up. Completely.
I actually like america a lot, but there are many things about its government that strike me as being completely fucked up.