What was the deadliest thing that happened in the civil war

The US Civil War: 750,000 (Estimated)

Burying the Dead on the Battlefield of Antietam, September 1862.

for the 2 countries u can do china and america because america has a democratic government while china has a communist government.

a democracy is a government run by the people either by directly voting or indirectly by electing representatives. an oligarchy is a government run by a few or a small group of people. a democracy and oligarchy are similar because both in an oligarchy and an indirect democracy, a small group of induvial determine the laws for a large group of people they are different because in an oligarchy it is easier to control and they do not have to answer to a large number of people in the country, unlike a democracy where they do have to answer to a large number of people an county that is a democracy would be the united states. a country that is an oligarchy would be the china.