Simplify the following text for a Grade 9 native English-speaking person.
Original: It depicts a seminal moment of the French revolution , when , on 20 June 1789 , deputies of the Estates-General met at the court and vowed that they would not disband before the proclamation of a formal Constitution for France .
Simplified: It depicts the formal announcement of the French revolution made in the Royal Tennis Court there on 20 June , 1789 .