What motivated other countries to join against France when the war started?

The motivation for other countries to join against France at the onset of the war was primarily driven by the realization that their own monarchies could also be threatened by revolutionary movements. The French Revolution, which began in 1789, introduced the radical idea that established monarchies could be overthrown and that the principles of democracy and popular sovereignty could lead to widespread upheaval. Monarchies across Europe, particularly those of Austria, Prussia, and Great Britain, grew concerned that the revolutionary ideals emerging from France might inspire similar revolutionary sentiments within their own borders, potentially leading to the destabilization or overthrow of their governments.

This fear was exacerbated by the fact that revolutionary France was positioning itself not only as a nation rebelling against tyranny but also as a beacon of change that could attract followers in other nations. Thus, these countries felt compelled to act in order to safeguard their own thrones and maintain the status quo in response to the radical changes happening in France. The threat was not just about military engagement; it reflected deeper anxieties over the stability and continuity of political authority within the existing monarchies.