India’s northeast, a lush triangle ringed by China, Burma, and Bangladesh is dotted with picturesque tea estates and pineapple plantations. Wild elephants and one-horned rhinos roam ancient forested migration routes.

But this week, the state of Assam (see map here) witnessed brutal mob violence, which virtually cut it off from the rest of India. According to police, at least 45 people have been killed, homes burnt, butchered bodies recovered, railway lines blocked in protest, and at least 150,000 people have fled their homes in fear.

At its heart, Assam’s troubles are about corrupt politicians encouraging illegal immigration at the expense of locals.

“Since 1971, there’s been a steady influx of immigrants from Bangladesh,” says Rahul Pandita, associate editor of Open magazine who’s covered India’s northeast extensively. “And local politicians gave them Indian identity documents so they would vote for them. They’ve changed the entire demographics of the area and created a powder keg ready to explode.”

It would be akin to state politicians in Texas inviting economic migrants from Mexico in exchange for votes, says Mr. Pandita, pitting migrants against their own citizens for jobs, education, and welfare benefits.

It’s an open secret that the northeast is the main entry point for millions of illegal Bangladeshi migrants into India. From there, they travel into Indian towns and cities, providing a cheap, useful work force. But in places like Assam, they also change electoral politics.

This week’s ethnic clashes involved one of Assam’s tribal communities—the Bodo people—against Bengali speaking Muslim migrants. The violence was initially sparked by the death of four Bodo men, but signifies a much wider conflict.

Meanwhile, with local police unable to cope, Assam called in Indian Army forces who were given “shoot on sight” orders to quell the clashes. By Wednesday evening, armed forces had shot dead five people.

But according to Pandita, brute force is no answer to this problem that’s been decades in the making.

“Millions of people are entering your country and you are appeasing them to the extent that your own citizens feel threatened,” he says. “A man who is 70 sees all these outsiders taking over all farmland, shops. His son has no ration card, no job, so he’s going to react. For short term electoral gain, politicians have created this problem.”