Tensions between India and Bangladesh have flared up after an alarming incident near their shared border. On Monday, a Bangladeshi diplomatic mission in Agartala, a city in northeast India, came under attack by activists protesting the arrest of a Hindu monk in Bangladesh. The protesters, angered by what they see as the mistreatment of Hindus in Bangladesh, stormed the mission, leaving its staff feeling deeply unsafe.

The very next day, Dhaka summoned India’s High Commissioner to Banglad...