In Montana's wilderness, man poses the greatest threat to drug smugglers crossing the Canadian/American border. Long winters, boredom and isolation, fuel addicts' urgency for drugs.

Kingston is in the hands of highly organized and warring drug gangs. They manage drug trafficking and distribution at all levels. With the patronage of politicians, they fight hard to protect their turf in a city where poverty and guns drive the drug trade.

Chicago, the biggest open-air crack and heroin market in America is at saturation point. The result: record levels of overdoses and homicides, as gangs fight over drug turf.

Houston's drug hub is the 'Bloody Nickel' - the Fifth Ward. Five square miles of 24/7 drug and party action. Gangs work across the ethnic divide to keep the drugs flowing; while cops and Cartels vie with each other for control.

Denver - the mile high city - has just legalized recreational use of Marijuana. The city's gang-banger dealers have battled falling profits since medical Marijuana became law, and forced them to push new products. This latest move is last straw.

Miami - once America's cocaine capital; but no more. The War on Drugs has hit home. Today dealers and users play cat and mouse with the cops and live in dread of the Feds. And a new look drug scene has gone underground.

In Kensington north Philadelphia, heroin, crack cocaine and PCP are dealt from a hundred different corners. Kensington is a giant drug drive thru. But for the addicts and dealers it's a deadly trap that threatens to drive them literally insane.

Since the days of Kurt Cobain and grunge music, Seattle has been nicknamed Junkietown. The city's liberal laws and high demand for drugs is attracting gangsters and dealers looking to get rich. From the competitive crack business in Belltown to fashionable Molly users on the electronic dance music scene, National Geographic explores the highs and lows of Seattle's drug business.

Phoenix, Ariz., is the wholesale drug capital of America, under the control of one of Mexico's most powerful and ruthless drug organizations -— the Sinaloa Cartel. Almost 200 miles north of the Mexican border, the city has become the major stopping off point for the large-scale distribution and transshipment of marijuana, heroin and methamphetamine up from Mexico and out to the rest of the country.

Music and drugs go hand in hand in Nashville. For musicians who don't make it, drugs are the easiest way to make a living. National Geographic talks to a user and freelance cook who makes methamphetamine at home to cover his costs and get high. Then, learn how the 19th Judicial District Drug Task Force is faced with cleaning up after meth cooks' — operations that are both extremely dangerous and prohibitively expensive.