There were many reasons. One being that it was winter and it was harder to gather things and keep spirits up when everyone was running low on food. It was also in bad weather.
Made government less centralized
Churchill led England during World War 2!
The United States feared that if communism was successful on Vietnam, the rest of the countries that border it would soon turn into communism and those other countries that border that new communist country would also be converted to communism and so on. This is called the "domino theory" and made the United States to send troops to prevent the theory from happening.
