The great event of Elizabeth's later years was the Seven Years' War. Elizabeth regarded the Convention of Westminster (16 January 1756) in which Great Britain and Prussia agreed to unite their forces to oppose the entry of or the passage through Germany of troops of every foreign power, as utterly subversive of the previous conventions between Great Britain and Russia. Elizabeth sided against Prussia over a personal dislike of Frederick the Great. She wanted him reduced within proper limits so that he might no longer be a danger to the empire. Elizabeth acceded to the Second Treaty of Versailles, thus entering into an alliance with France and Austria against Prussia. On 17 May 1757 the Russian army, 85,000 strong, advanced against Königsberg.