Rome was declared the capital of Italy in March 1861, when the first Italian Parliament met in the kingdom's old capital Turin in Piedmont. However, the Italian Government could not take possession of its capital, because Napoleon III kept a French garrison in Rome protecting Pope Pius IX. By the September Convention of 1864, Napoleon III agreed to withdraw French forces from Rome in return for Italy respecting the borders of the rump Papal States. French forces were withdrawn by 1866, but their absence encouraged Garibaldi to launch a renewed attempt to take Rome and French troops returned, defeating Garibaldi's expedition at the Battle of Mentana. The opportunity to eliminate the last vestige of the Papal States came when the Franco-Prussian War began in July 1870. Emperor Napoleon III had to recall his garrison from Rome for France's own defence and could no longer protect the pope, following the collapse of the Second French Empire at the battle of Sedan.