Question (Lots of different responses):
Why did rates of disease transmission increase so rapidly in the first part of the 20th century?
World War I, and to a lesser extent, World War II, brought soldiers all over the world and then back home. The Spanish Flu pandemic is the most severe result of these transmissions.
Other good answers:
• New transportation technology like airplanes
• Poor hygiene
• Misunderstanding of scientific principles of disease transfer
• Poverty/poor living conditions