Which killed the greatest number of American soldiers during the Spanish-American war?

a. Invasion of Puerto Rico

b. Battle of Manila Bay

c. yellow fever

d. Battle of San Juan Hill

The correct answer is C. Yellow fever

The war was brief and a landslide victory for the United States. Most of their soldiers who became casualties did so due to the yellow fever which was difficult to contain and not due to deaths in battle. It kept spreading and huge numbers got infected.