The United Nations Office of Drugs and Crime says in a new report that global opium production has reached record levels not seen since the 1930s, mainly due to increased cultivation in Afghanistan.

Thomas Pietschmann, co-author of the U.N. report, says it is meant as a warning that the world is sitting on vast amounts of opium, not all of which has reached drug users.

That opium could make its way to the streets of Europe, Russia and Southeast Asia over the next few years and increase the number of deaths related to opium and heroin, which is also derived from the opium poppy plant.

The main reason for the increased opium yield is instability in Afghanistan, where Taliban militants are pressuring farmers to grow the plant.

“Taliban has used it to fuel many of its activities. It’s one of its main sources of revenue,” says Michael Kugelman, senior program associate for South and Southeast Asia at the Woodrow Wilson International Center for Scholars in Washington, D.C. 

“Farmers in Afghanistan … are pressured, intimidated and threatened by violence … if they don’t keep up with poppy production,” Kugelman says.

With most foreign troops now out of Afghanistan, especially since the end of 2014, and instability growing, farmers are also increasingly planting opium poppies for their own economic survival. 

It is a practice they have employed for decades, despite $8 billion in efforts by the U.S. to reduce opium cultivation. Pietschmann says those efforts in Afghanistan worked, at first, by convincing farmers to plant other crops. Some farmers switched after being shown that they could still make money planting other crops. 

“It’s a really market-driven approach, but at the same time, really helping and assisting the farmers to change their mindset,” Pietschmann says.

But, he says, that approach needs stability, which is something Afghanistan currently lacks.