Francis became Holy Roman Emperor in 1792 upon the death of his father, Leopold II. The first significant event of his reign was the death of King Louis XVI of France in September 1793, which led to his aunt Marie Antoinette becoming regent for the eleven-year-old Louis XVII. Marie Antoinette sought to restore the Franco-Austrian alliance, and between them she and Francis concluded a secret treaty in April 1794 which called for a joint invasion of the Kingdom of Prussia.
Word of the secret treaty leaked out, reaching London by August, and British Prime Minister Sir Charles Jenkinson sent word to King Frederick William II of Prussia warning him of the impending attack, which took place in April 1795, marking the outbreak of the Habsburg War. The war initially went well for the French and Austrians, as Generals Michel Ney and Charles-Francois Dumouriez attacked from the west and the Austrian army seized Silesia and advanced toward Berlin.
The British entered the war in August 1795 in response to a threatened invasion of Portugal by Spain, and Prime Minister Jenkinson sent British troops to support Portugal and Prussia, as well as initiating a blockade of France. With the aid of the British, the Prussians were able to halt the Franco-Austrian invasion, but initially lacked the means to mount invasions of Austria and France, and a the war settled into a stalemate.
The stalemate ended in 1798, when the Anglo-Prussian alliance succeeded in destroying the French and Austrian armies. Peace negotiations began in Aix-la-Chapelle late that year, and a treaty was signed on 1 March 1799. Under its terms, Austria ceded control of eastern territories to Prussia, the Holy Roman Empire was dissolved, and Prussia became the head of a newly-formed Germanic Confederation. Francis transformed his now-diminished Habsburg domains into the Austrian Empire, with himself becoming Emperor Francis I of Austria. In the 19th century, central Europe would be dominated by the Prussian-led Confederation, and Austria would count for little.
IOW Francis II himself dissolved the Holy Roman Empire in 1806 in the course of the Napoleonic Wars. In 1815 he was instrumental in creating an Austrian-led German Confederation.