Final answer:
The U.S. government increased involvement in Vietnam due to the Gulf of Tonkin incident.
Step-by-step explanation:
The correct option for the U.S. government increasing involvement in Vietnam is B. the Gulf of Tonkin incident. This incident occurred in 1964 when the USS Maddox, an American destroyer, was allegedly attacked by North Vietnamese forces in the Gulf of Tonkin. This event led to the passing of the Gulf of Tonkin Resolution, which gave President Lyndon B. Johnson broad powers to escalate the U.S. military's involvement in Vietnam.
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