A terrible flood has hit Bangladesh, affecting millions of people. Many in Bangladesh are pointing fingers at their neighbor, India, accusing it of causing the disaster by opening a dam on a shared river. But India says it had nothing to do with it.

The floodwaters came rushing through after Bangladesh claims India opened the Dumbur dam, which sits on the Gumti River in the Indian state of Tripura. This state shares a long, 800-kilometer border with Bangladesh, making the river important...