Complex sentence: On 18 March 1871, the Paris National Guard, which largely came from working-class neighborhoods, elected its own officers and had become politically radicalized, refused to hand over its arsenal of cannons to the French regular army, and killed two army generals.
Split into simpler sentences: On 18 March 1871, the Paris National Guard, which largely came from working-class neighborhoods, elected its own officers and had become politically radicalized. It refused to hand over its arsenal of cannons to the French regular army, and killed two army generals.