6. Tangshan Earthquake, China (1976)
This one actually is the deadliest earthquake of the 20th century, and proved once again that what makes earthquakes so lethal isn't always the force itself, but the infrastructure of the area it hits. The 7.8-magnitude event struck during the middle of the night on July 28, and leveled 92 percent of the residential buildings in this city of over a million.
Food, water, and other resources became scarce as survivors worked to rescue people from under the rubble, but with all but one road destroyed -- and train rails bent and bridges collapsed -- help was long to come. Nearly a quarter of a million people died either during the quake or in the days following, some from starvation, some from dehydration, and still others from the disease that descended as already-buried bodies became exposed when rain washed away the dirt.