<em>What indicated that the United States had been secretly involved in Vietnam before its official involvement was the Pentagon Papers. </em>
The United States Department of Defense had a secret report about military involvement in the War of Vietnam. They called the Pentagon Papers. Daniel Ellsberg, a military analyst in the case, considered in 1968 that the information should be released to the public. In March 1971, he gave a copy of the papers to the New York Times. The papers showed how previous administrations had misled public information about the involvement of the US in Vietnam.
The other options of the question were A) the 26th Amendment, C) the 1973 cease-fire, and D) Vietnamization.
The pentagon papers is a report of the Department of Defense detailing the involvement of the United States' military on Vietnam from 1945 to 1967. The papers were first brought to public by the New York Times in 1971. The papers showed that the Johnson administration had lied about the scope of its actions in the Vietnam War.
Chinese rulers claimed they had the "Mandate of Heaven" which gives them the ability to rule over China. Even earlier rulers claimed that they were a god in the flesh or a descendant of one.
