Armies of young insurgents are changing the course of a forgotten war

Two loudspeakers, as big as the men carrying them, are brought to the rocky hilltop. Some 800m below, in the town of Hpasang, lies a sprawling Myanmar army base.

It’s a blisteringly hot day - above 40C - and behind, on bamboo poles, more young resistance fighters carry a large, heavy battery pack and amplifier. Leading the ascent is Nay Myo Zin, a former army captain who, after 12 years in the military, defected to the resistance.

With his dark green camouflage jacket draped over one shoulder, he has the...