Under Frederick William II's weak rule (1786-.1797) Prussia had undergone a serious economic, political and military decline. His successor king Frederick William III tried to remain neutral during the War of the Third Coalition and French emperor Napoleon's dissolution of the Holy Roman Empire and reorganisation of the German principalities. Induced by the queen and a pro-war party Frederick William joined the Fourth Coalition in October 1806. Napoleon easily defeated the Prussian army at the Battle of Jena and occupied Berlin. Prussia lost its recently acquired territories in western Germany, its army was reduced to 42,000 men, no trade with Britain was allowed and Berlin had to pay Paris high reparations and fund the French army of occupation. Saxony changed sides to support Napoleon and joined the Confederation of the Rhine. Ruler Frederick Augustus I was rewarded with the title of king and given a slice of Poland taken from Prussia.