It killed 1/3 of the population of Europe and people wanted cleaner cities to prevent this from happening again
Answer: The main reason for America sending combat troops to Vietnam in 1965, was to follow the Truman Doctrine and contain Communism, the Americans strongly believed in the Domino theory.
According to the CIA world Fact book, out of the 40 poorest countries in the world in 2010, 84% of them were former colonies of European Empires.
These included world powers such as Britain, France, Spain, Netherlands etc.
The colonial powers used a vast network of shipping and logistics to exploit local resources which made European countries extremely rich.
Countries such as Spain imported Gold, Potatoes, Peppers from South America and sold them all over the world, while the British Empire used India's immense human capital for farming and cheap manufacturing.