The Estates-General was a meeting called by King Louis XVI, he called the meeting because the French government had financial problems.
It was considered a failure because the representatives of the First and Second Estates - clergy and nobility respectively - wanted to separate from the Third Estate - the bourgeoise and commoners -. They wanted to block any reforms to the privileges they had, for example, taxation.
The Third State called the Estate-General to reunite with them, sit as one body and move to the indoor tennis court at Versailles. They called themselves National Assembly and wanted to develop a new constitution for France.
The king had to accept the legitimacy of the National Assembly and this pushed the French Revolution beyond the King’s ability to control it.