The meeting of the Estates-General in 1789 helped trigger the French Revolution by causing the Third Estate to break away and form its own governance system, the National Assembly. The Third Estate was unhappy about the voting representation of the three estates.
The First Estate was the clergy, and the Second Estate was the nobility. The Third Estate was the rest of French society. Each estate got one vote in the Estates-General, even though the Third Estate was vastly larger than the First and Second Estates. The Third Estate was nearly always overridden by the combined votes of the clergy and nobility. The Third Estate broke away and formed the National Assembly to get more liberty and a more equitable tax burden.