What Are the Reasons to US Involvement in South Vietnam?

What can you learn from Source A about the reasons for US involvement in South Vietnam?
Source A is an extract from a book written by Senator John F Kennedy in 1956 (four years before his presidential election). The source outlines the American domino theory, a label given to the American foreign policy in South East Asia, in which it was believed that because of the countries geographical closeness the communist influence in china would increase and conquest neighbouring countries Burma, Thailand, India, Japan, Philippines, Laos and Cambodia,.
The source is intended for public use; therefore we are able to learn what the US government wanted the public to believe.
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