Which event in 1789 marked the beginning of the French Revolution?

The Storming of the Bastille on July 14, 1789, is widely recognized as the event that marked the beginning of the French Revolution. This act symbolized the uprising against the monarchy's oppression and the demand for liberty and justice by the people of Paris. The Bastille, a fortress prison, was seen as a powerful emblem of the tyranny of the Bourbon monarchy. When revolutionaries seized the prison, it was a pivotal moment that galvanized public support for the revolutionary cause, leading to widespread uprisings across France.

In contrast, the other choices represent significant developments in the revolution but not the initial spark. The execution of Louis XVI occurred later, in 1793, as a result of the revolution's progression toward more radical measures. The Declaration of the Rights of Man and of the Citizen was adopted shortly after the storming of the Bastille, in August 1789, as a foundational document that articulated the principles of the revolution. Similarly, the formation of the National Assembly took place earlier in June 1789 when the Third Estate declared itself the legitimate representative body of the French people, setting the stage for future developments but not serving as the initial event of the revolution itself.