The Mexican drug cartels battling viciously to expand and survive have a powerful financial incentive: Across the border to the north is a market for illegal drugs unsurpassed for its wealth, diversity and voraciousness.
Homeless heroin addicts in big cities, "meth heads" in Midwest trailer parks, pop culture and sports stars, teens smoking marijuana with their Baby Boomer parents in Vermont - in all, 46 percent of Americans 12 and older have indulged in the often destructive national pastime of illicit drug use.
This array of consumers is providing a vast, recession-proof, apparently unending market for the Mexican gangs locked in a drug war that has killed more than 10,780 people since December 2006. No matter how much law enforcement or financial help the U.S. government provides Mexico, the basics of supply and demand prevent it from doing much good.
"The damage done by our insatiable demand for drugs is truly astounding," said Lloyd Johnston, a University of Michigan researcher who oversees annual drug-use surveys.
The latest federal figures show that 114 million Americans have used illegal drugs at some point - and 20 million are current users.
Marijuana is by far the No. 1 drug, sampled by 100 million Americans, including nearly half of high school seniors. But more than 35 million Americans have used cocaine at some point and 34 million have taken LSD or other hallucinogens.
"It's a drug dealer's dream - sell it in a place where he can make the most money for the risk taken," said Dr. H. Westley Clark, director of the federal Center for Substance Abuse Treatment.
"There's a tremendous amount of denial until you're face to face with it," Clark added. "A substance abuser can be anybody. Everybody is at risk."
The Mexican cartels are eager to feed this ravenous appetite. Once used mostly to transship drugs from South America, Mexico is now a major producer and distributor; its gangs control cocaine networks in many U.S. cities and covertly grow marijuana on U.S. public lands.
For now, the Mexican government is fighting the cartels and working with U.S. authorities who have promised to stop the southbound flow of weapons and cash - but all parties are aware of the role played by the U.S. market.
"When the U.S. government turns up the pressure a lot, then is when you see a return to the old formula of saying (to Americans), 'You also have corruption, you consume the drugs, you're the biggest drug consumer in the world,' " said Jose Luis Pineyro, a sociologist at Mexico's Autonomous Metropolitan University.
Gil Kerlikowske, a former Seattle police chief recently appointed by President Obama to be U.S. drug czar, said the Mexicans "make an excellent point."
"Our drug abuse causes problems elsewhere - our per capita consumption is very high," said Kerlikowske, who argues that reducing demand through education and treatment is as vital as border interdictions in quelling Mexico's drug violence.
Country of origin didn't matter much to David Hart. Hart, 49, said he started using drugs at 14 and didn't stop until he entered a one-year recovery program in January at the Springs Rescue Mission in Colorado Springs, Colo.
The son of an alcoholic father, Hart moved from Arizona to Colorado in 1993. A promised construction job didn't materialize, and since then he's mixed part-time work with stints of homelessness, panhandling to pay for hits of crack, marijuana and speed.
"When you're depressed about your lot in life, and angry about the way you've been treated, drugs are a perfect way out. You smoke that crack and your problems just go away. You know they're going to come back, but for that brief moment you don't have to deal with it."
He's grateful to his supporters at the recovery program, but unsure what lies ahead.
"It's been a part of my life for so long," he said. "It's going to be a challenge for the rest of my life to stay clean."
Yet Hart is, in some respects, lucky. Federal figures indicate that roughly 7.5 million Americans needed treatment for illegal drug abuse in 2007, and only about 1.3 million received it.
The Rescue Mission's CEO, the Rev. Joe Vazquez, said Hart is part of a wave of drug-abusing transients who've settled into the netherworld of an outwardly prosperous region.
"There's this whole segment of our community living well below what their creator created them for - these men coming with a toolbelt and backpack, living in little rundown motels, struggling with addiction," Vazquez said.
Federal surveys reveal cyclical trends in drug abuse - but the number of lifetime users keeps growing. Overall abuse rates were highest in the 1970s, declined through the early '90s, went back up and now seem to have stabilized over the past six years.
Studies of youth drug use in Western Europe show a few countries with serious problems, but overall a far lower portion of young people there are abusing drugs than in America. Elsewhere around the world, drug use also is widespread, though data is generally not as thorough as in the United States.
"There's no escaping the fact that we have the highest drug rates in the world," said Craig Reinarman, a sociologist at the University of California, Santa Cruz.
U.S. authorities were encouraged that drug use among 12-to-17-year-olds declined by about 25 percent between 2002 and 2007. But Johnston, the University of Michigan researcher, says his latest student survey suggests the decline halted in 2008, and he is concerned by data showing that fewer students view smoking marijuana as a serious risk.
There was no similar recent drop-off of drug abuse among the biggest demographic category - young adults aged 18-25. Illicit drug use also has surged among those aged 55 to 59 - baby boomers whose young adulthood coincided with the drug culture's heyday. And there is deep concern about increasing abuse of prescription medicines among all age groups.
Survey after survey shows the vast scope of illegal drug use - deep-rooted in all regions, among all races and socio-economic groups. Big cities indeed have severe problems, but the states with the highest overall abuse rates include Rhode Island, Vermont, Montana and Alaska.
"There's this assumption that drug abuse is more common in racial minorities, especially blacks," said Dr. Wilson Compton, a division director at the National Institute on Drug Abuse. "It's not true. Either the rates are lower or at least no higher."
Reinarman reflected on the recent methamphetamine outbreak across the American heartland - Iowa, Missouri, Kansas and elsewhere.
"Here they live in crummy little houses, in towns that are dying ... and along comes a drug that provides a great rush," he said. "You can't separate drug problems from the broader matrix of social and personal problems. You can't have a drug policy that works unless it's part of a much broader social policy."
For those concerned about marijuana, Vermont is an active front line, with the nation's highest rates of pot usage. It's one of several regions where joints may now be more prevalent among teens than cigarettes.
"People say, 'It's easier for me to get pot than to buy a beer,' " said Barbara Cimaglio, deputy commissioner of the state Health Department's Division of Alcohol and Drug Abuse Programs.
Annie Ramniceanu, clinical director at Spectrum Youth and Family Services in Burlington, Vt., says many of the 350 youths her agency counsels annually started smoking pot before their teens.
"They just get high all the time," she said. "They never learned how to have fun without smoking pot, never learned how to deal with conflict, how to focus on anything."
In both blue-collar and affluent families, she sees multigenerational problems.
"It's become the cultural norm for these families, where drug use is absolutely no big deal," she said. "The kids smoke with their parents, or know their parents use other drugs."
Another drug counselor, Yolanda Morales of New York City, is cautiously upbeat about the attitudes she observes among young people.
Now 55, Morales lapsed into a cocaine habit and a 15-year addiction while trying to juggle graduate school and a job. She spent five years in federal prison for trafficking, got out in 2003, and now works for the Fortune Society in New York, counseling other ex-offenders.
She has shared her story candidly with her college-bound daughter.
"When I was in school in New York, people stood on the corner selling drugs - no one gave a damn," Morales said. "The consequences of that era has the younger generation a little more scared. I don't see them doing the hard drugs like we were. They're more informed - there's more wariness about trying different stuff."