President Barack Obama heads to Mexico to meet with new President Enrique Peña Nieto this week, and the ongoing joint effort to combat drugs and organized crime is likely to be part of the conversation. But the visit also comes just as the discussion surrounding the so-called "war on drugs" has begun to shift among Latin American leaders, as Jonah Engle argues in his new article for Foreign Policy. In "Blow Back," Engle paints a vivid picture of the drug-torn regions of Colombia -- one of America's staunchest allies when it comes to fighting trafficking. As drug-related violence and instability across the region have continued to worsen, prominent Latin American political figures have begun to rethink the last 30 years of international drug policy. "It wasn't supposed to be this way," Engle writes. Above: Though it appears on the surface to be a poor city, Buenaventura, Colombia's biggest port, is considered the "jewel in the crown" for drug traffickers. "Whoever controls access to this port, in criminal terms, is able to hide drug consignments in the tens of thousands of containers that leave those facilities every week and go all over the world," InSight Crime co-director Jeremy McDermott told Engle. As trade at the port has increased, it has become harder for customs officials to inspect all the cargo shipped from Colombia to the United States, Engle says. In this photo, an engineer looks at the seaport in Buenaventura, department of Valle del Cauca, Colombia, on Feb. 26, 2013. Buenaventura has been riven by gang warfare over control of trafficking routes, with the powerful Colombian drug cartel known as the Urabeños trying to push its rival, the Rastrojos, out of the port. There are imaginary borders, and if anyone crosses that border who isn't from that area, they will kill you. It's that simple," one Buenaventura resident told Engle. Thousands of residents have been displaced by the conflict. Above, a Colombian soldier patrols in a poor neighborhood of Buenaventura, on Nov. 9, 2006. In late 2011, Colombian President Juan Manuel Santos became one of the first sitting world leaders to oppose the war on drugs. "A new approach should try and take away the violent profit that comes with drug trafficking," Santos told the Observer in 2011. If that means legalizing [drugs] ... I will welcome it. According to Engle, up to that point, most Latin American leaders who urged their countries to rethink drug policy had waited until retirement. In this photo, taken on Feb. 22, Santos arrives at the Justice House in Commune 13, one of the shantytowns in Medellín, Colombia with the highest rates of urban violence and displacement due to disputes between gangs. Though the Medellín cartel was dismantled after Pablo Escobar's death in 1993, according to Engle, new paramilitary groups continued to fill the void. In this photo, gangsters get ready to sniff cocaine at Commune 13 in Medellín, on Feb. 6, 2010. Gustavo de Greiff, the Colombian attorney general who brought down Escobar, told Engle, "We killed Escobar. We dismantled many, many small cartels and nothing happened. Cocaine continues to flow into the United States, and the narco-traffickers getting rich. In this photo, Colombian soldiers patrol Commune 13 on March 20, 2013 in Medellín. So far this year, more than 335 people have been killed by urban conflict and more than 400 have been displaced, joining the some four million people in Colombia who have been internally displaced due to drug violence. To confront the violence, the government has brought 1,000 new policemen into the region. Colombia is the only country that allows aerial fumigation of drug crops. Engle mentions that communities living next to coca crops strongly oppose the policy. They claim that the glyphosate that government planes spray onto coca fields negatively impacts trees, animals, and rivers in surrounding areas. Above, a man covers his face as he stands next to a truck burned during a protest staged by farmers in the Taraza municipality, Antioquia department, on Oct. 5, 2011. More than 2,000 farmers from different regions arrived at Taraza to protest against the Colombian government and to demand it cease fumigation of illicit crops with glyphosate. Manuel Rodríguez, Colombia's first environment minister, authorized aerial spraying of drug crops in the early 1990s under strict guidelines, Engle writes. But according to Engle, Rodríguez thinks that the government has become lax in abiding by these regulations -- perhaps part of the reason the public has grown so outraged at the practice. In this photo, another taken during the Oct. 5, 2011, farmers' protest against aerial fumigation of illicit crops, a Colombian farmer and his children rest outside the Coliseum in Taraza. Farmers demanding the end of the fumigation program clash with riot police during a protest in Taraza on Oct. 7, 2011. While U.S. officials say the yield of Colombian coca bushes is decreasing, the most recent U.N. figures tell a different story, showing that reductions have leveled off at around 60,000 hectares of coca, Engle writes. Production has also been pushed into parts of the country where the state is weakest, particularly the southwest. In 2011, coca cultivation increased 23 percent across the southwestern department of Cauca and its neighboring departments, Engle notes. Together these areas are home to more than half the country's coca fields. Above, a farmer harvests coca leaves in a coca plantation in the mountains of Cauca on June 21, 2012. The department of Cauca has become an important base for Colombia's largest rebel army, the Revolutionary Armed Forces of Colombia (FARC), which profits from the drug trade. The heavily militarized region is packed with security checkpoints and government forces. In this photo, Colombian police officers stand guard behind assault rifles seized in Cali, Colombia, on March 5, 2010. The Colombian police had recently seized 234 Chinese-made assault rifles (220 type M-16 and 14 type AK-47 replicas), which had been bought by the Rastrojos drug gang. FARC commander Ancizar, a.k.a. Monazo, looks on before reading a statement confirming the capture of French journalist Romeo Langlois as a "prisoner of war" in Caqueta department, which neighbors Cauca, on May 5, 2012. Langlois, a 35 year-old reporter for France 24, had been accompanying Colombian soldiers who destroyed five cocaine production labs, and went missing after a firefight between the FARC and government soldiers. He was later released after 33 days in FARC custody. A drug addict shoots heroin in "El Calvario," a place where drug addicts come together to consume drugs, in downtown Cali, Colombia on April 3. Colombian President Juan Manuel Santos has given police 60 days to shut down sites like these around the country. Above, Henry de Jesus Lopez Londoño, a leader of the Urabeños cartel, is shown in the custody of Argentine Federal Police on his way to court in Buenos Aires on Oct. 31, 2012. Colombian soldiers patrol the Cajambre river, near Buenaventura, on May 29, 2012, after a homemade submarine with a capacity to transport up to five tons of drugs was seized by the Colombian Navy. Felipe CAICEDO/AFP/GettyImages A Colombian soldier walks away from the burning remnants of a makeshift submarine allegedly belonging to the Rastrojos, which was discovered near completion in Majagual, Colombia on Feb. 16, 2010. The submarine would have been able to carry eight to 10 tons of drugs at a time. A Colombian anti-narcotics policeman surveys an illegal laboratory producing cocaine hydrochloride on Oct. 13, 2011 in Puerto Gaitan, Colombia. The huge 34-building laboratory was capable of producing between 500 and 800 kilos of cocaine per week. Engle writes, "While cocaine use is down in the United States, it remains the world's biggest consumer -- and according to U.S. government statistics, Colombia continues to supply 95 percent of the American market." Above, a Colombian police officer stands guard next to packages of seized cocaine during a press conference at a police station in Apartado, Colombia, on April 20, 2013.