The United States became involved in Vietnam
because Americans feared that

Because of communism...

Explanation:

After the assassination of President Kennedy in 1963, Lyndon Johnson became the new President of the USA. He referred to the domino theory, by which he meant that if Vietnam became a communist country, other countries in South Asia might follow its example, much like one domino sets off another until they have all fallen down. Johnson decided to send American soldiers to the war in Vietnam to prevent this from happening.

d.he wanted to send diplomats to communist countries.

frederick william of brandenburg-prussia trained his son, frederick, to be a hardy soldier. but frederick disliked rifle shooting and horseback riding. unlike his father, he was interested in french literature. he enjoyed poetry and music and, like some others of the enlightenment, he scoffed at religion. his father thought him soft, frivolous and unmindful of his duties. and when frederick refused to put his signature on a right to succession, for a few moments his father strangled him.