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.

the assassination of president lincoln was just one part of a larger plot to decapitate the federal government of the u.s. after the civil war. the first reaction to lincoln’s death was disbelief. then it quickly changed to grief. abraham lincoln’s death created an outpouring of grief from citizens in both the north and the south.

explanation:

lincoln was the first u.s. president to be assassinated. president abraham lincoln, america’s civil war leader, was assassinated just five days after confederate general robert e. lee surrendered his army at appomattox court house, ending the four-year war between the states. on the evening of april 14, 1865, lincoln was attending a performance of our american cousin at ford’s theatre in washington, d.c. john wilkes booth – a 26-year old actor, confederate sympathizer, and white supremacist – slipped into the presidential box and shot lincoln in the head. john wilkes booth and his conspirators had initially planned to kidnap lincoln to save the confederate states. but as the confederacy faltered, booth’s thoughts turned to murder. booth may have decided to act on his hatred after lincoln endorsed giving the right to vote to african-american men who had served in the union army.