Complex sentence: The key figure was Holy Roman Emperor Leopold II, brother to the French Queen Marie Antoinette, who had initially looked on the Revolution with equanimity, but became more and more disturbed as the Revolution became more radical, although he still hoped to avoid war.
Split into simpler sentences: The key figure was Holy Roman Emperor Leopold II, brother to the French Queen Marie Antoinette, who had initially looked on the Revolution with equanimity. He became more and more disturbed as the Revolution became more radical, although he still hoped to avoid war.