A MIT SHAH, India’s home minister, calls them “termites” and “infiltrators”. The government will hunt them down and throw them into the sea, he thunders. Unfortunately, it is not just the standard bluster from a nativist politician railing against illegal immigration. Last year bureaucrats in the Indian state of Assam, which has a population of about 33m people, produced a list of more than 4m of its residents whom they consider foreigners, without any right to live there. A further 100,000 people were deemed non-citizens in June (see article).

Mr Shah insists that all these people will be deported. In practice, neighbouring Bangladesh, from which they are said to have migrated, will not accept them, since in most cases there is no evidence that they are anything other than Indians too poor and uneducated to navigate the complex bureaucracy of citizenship. But even if the threatened mass deportations never take place, the process of declaring people aliens, and hauling lots of them off to internment camps, is not only a rank injustice, but also a threat to stability. The supposed illegal immigrants are overwhelmingly Muslim. The purge is therefore exacerbating sectarian tension in a state that saw bloody Hindu-Muslim riots as recently as 2012, when some 400,000 people were displaced. Yet Mr Shah considers the campaign in Assam against illegal immigrants such a success that he wants to replicate it throughout the entire country.

Indigenous Assamese have long complained that they are being swamped in their own homeland by migrants from Bengal, the densely populated region to the south (see article). In colonial times, there was such an influx, since there were no borders to stop poor Bengalis moving north in search of a better life. Assamese nationalists, pointing to Bengalis’ ever higher share of the state’s population, insist the flow of migrants continues to this day, even though the Muslim part of Bengal has become a separate country, Bangladesh.