Others who push for global decriminalization of marijuana laws also said that U.S. efforts to pressure foreign nations over marijuana would weaken.

“It really is a game changer. It places the U.S. in a very different place,” said Kasia Malinowska-Sempruch, the director of the global drug-policy program of the Open Society Foundation, a New York-based group funded by liberal financier George Soros. “This clearly says the paradigm is shifting.”

Jelsma said that if U.S. states such as Colorado and Washington could impose a regime of control on marijuana that didn’t cause usage to soar, “it could mark a snowball effect on Latin America.”

Among those unhappy with moves to legalize marijuana are likely to be Mexican organized-crime groups, which earn billions of dollars a year smuggling pot to the United States. A study published last month by the Mexican Institute for Competitiveness, a nonpartisan research center that examines the effects of globalization, said that as much as a third of crime groups’ revenue came from smuggling pot.

Hope, a co-author of the study, said crime groups, particularly the powerful Sinaloa Cartel, could “lose 24 percent of their gross export revenues” as U.S. states softened laws on marijuana.

“This would reshape the Mexican criminal underworld in interesting ways,” he said, including slashing the number of jobs involved in smuggling an estimated 2,000 tons of marijuana northward each year.

Hope said, however, that the impact would be biggest in the political sphere.

“This will embolden some voices in the Americas calling for a change in policies,” he said.

Several former Latin presidents have signed statements criticizing U.S. counter-drug policy, including former President Fernando Henrique Cardoso of Brazil, former Colombian leader Cesar Gaviria and former Mexican President Ernesto Zedillo, all of whom have called for legalizing marijuana.

Castaneda, who also has signed the statements, said U.S. pressure on Latin nations to deploy soldiers to fight drugs would look inconsistent as some states allowed residents to use marijuana legally.

“It will look more and more contradictory, and even aberrant, that on one hand Mexico racks up 60,000 dead under (President Felipe) Calderon while on the other side Americans are going for legalization of, at least, marijuana,” he said.