Every spring, mason Mohammad Ghulam Sarwar boards a train to Indian Kashmir, seeking higher wages despite the risk of being targeted by militants in the disputed Himalayan region. Sarwar, 25, is one of an estimated half a million migrant workers who stream into the Himalayan region each year, forming the backbone of an economy increasingly reliant on labour from some of India’s poorest states. The dependence has endured despite decades of insurgency and a series of militant attacks that have...