The french national assembly swore the tennis court oath which was

a vow to continue to meet until they had produced a French Constitution.

Explanation:

The resentment of the Third Estate comprised about 98 percent of the French population and they still could be outvoted by the other two Estates comprised of clergy and nobility, which formed only 2 percent of the population. This unequal representative made the Third estate to form the National Assembly. Dispersed by the King, the National Assembly met at tennis ground to take oath to produce a written Constitution.