AGADEZ, Niger — In four years, Europe has cut down its illegal migration flow by almost 90 percent from its peak in 2015, and it has countries like Niger to thank for the dramatic drop.

For years, migrants from West African countries used Niger as a crossing ground on their way to Libya and then onto Europe. But in 2016, under mounting pressure from the EU, Niger began criminalizing immigration and patrolling the deserts for illegal crossings.

“The road is practically closed because of the police,” John Okoroafor, who traveled from Nigeria only to end up imprisoned in Agadez, told VICE News. “They are not taking anything for granted.”

For the EU, this arrangement has led to a dramatic decrease in refugees and migrants on their doorstep. For Niger, it’s meant a 1 billion–euro aid and defense package. But the success comes at a heavy cost: Niger’s jail cells are now packed with migrants and refugees. And the increasingly harsh policy has given birth to a new underworld of illegal activity that EU politicians warn could be creating even bigger problems for the region.

“It has gone underground,” Malin Björk, a member of the European Parliament from Sweden, told VICE News of Niger’s migration economy. “We have seen a larger and more organized network so that more organized crime is taking over. And that certainly can’t be seen as a security progress in any way.”

Niger says drug smuggling, for example, has soared over the last two years. In the country’s capital Niamey, officials showed VICE News a basement packed to the brim with illegal drugs they’d confiscated recently. They also warned that weapons trafficking is on the rise as a result of the new immigration policies.

VICE News traveled to Niger to speak to both authorities and smugglers about the EU’s evolving immigration policy and the new trafficking businesses it’s spawned.