Mexican cartels overpower police with ammunition made for the US military

On the morning of Nov. 30, 2019, a convoy of pickup trucks carrying men armed with a heavy machine gun and powerful .50-caliber rifles entered the Mexican town of Villa Unión and opened fire.

The men had been sent on a mission of intimidation: They planned to set fire to the town hall. Their superior firepower pinned down state and local police officers as they waited for military reinforcements. Terrorized residents scrambled to take cover from the hail of bullets.

Luis Manzano...