What was the gulf of tonkin resolution?

 The Gulf of Tonkin Resolution was a resolution by Congress that allowed President Johnson to expand US involvement in Vietnam.

Explanation:  The Gulf of Tonkin Resolution was passed by Congress in August, 1964, after alleged attacks on two US naval ships in the Gulf of Tonkin.  The key wording in the resolution said:

That resolution served as a blank check for President Johnson to send troops to whatever extent he deemed necessary in pursuance of the war.  Between 1964 and the end of Johnson's presidency in 1969, US troop levels in Vietnam increased from around 20,000 to over 500,000.

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