Why did European monarchs declare war on France during the French Revolution?

a.) to protect the endangered aristocracyB.) to end the persecution of the former monarchC.) to stop the new ideals of freedom and equalityD.) to gain control and influence over another area

All of these are true in a sense, but the best answer is B. King Louis XVI was married to Marie Antoinette, who was Austrian royalty. Both of them were persecuted by their own people during the French revolution. Since Marie was tied to Austria, and they can't have their daughter being harassed, Austria stepped in.

Other nations would also step in for different reasons. Some wanted to protect the idea of a monarchy, to prevent their own people from getting ideas. Others wanted a piece of France while it was fighting its own civil war.

a.) to protect the endangered aristocracy

Explanation:

The European nations watched with apprehension the course taken by the political unrest that was taking hold of France. A few years after the outbreak of the revolution in France, the popular strata of other absolutist nations like Switzerland, Holland, and Belgium began to sympathize with the principles and changes espoused by the French experience and wished to protect the threatened aristocracy. In this way, the monarchs of different European powers mobilized in a powerful counterrevolutionary movement.

Several monarchs announced the possibility of promoting an invasion of France, the Prussian and Austrian troops declare war against the Revolution. Acuadas, the French leaders announced the "homeland in danger". With that, it was decided to distribute arms to all the French population and the obligatory presentation of all the men apt for the fight.