Why did Louis XVI and the National Assembly decide to invade Austria?

The politics of the period inevitably drove France towards war with Austria and its allies. The King, many of the Feuillants, and the Girondins specifically wanted to wage war.

- The King was hoping war would increase his personal popularity and make him stronger.

- The Girondins wanted to export the Revolution throughout Europe and, by extension, to defend the Revolution within France.

- Other Monarchs from Prussia, Austria were threatening of invading France on the behalf of the French Monarchy. Moreover, the king was unhappy to sharing power and not wanting to accept the limitation on his power as result he agitating with the foreign monarchs

- People like Barnave and Robespierre in France opposed the war, and in Austria the emperor Leopold II, brother of Marie Antoinette, may have wished to avoid war, but unfortunately he died on 1 March 1792.

Thus France under this circumstance it preemptively declared war on Austria (20 April 1792). Prussia joined the Austrian side a few weeks later. And the wars that will catapult Napoleon into notoriety was on.