At the end of the Napoleonic Wars, the Congress of Vienna (1814-15) accorded Neuchatel an unstable dual status as a canton in the reorganized Swiss Confederation and as the personal property of the king of Prussia. The dissatisfied Swiss, caught up in the spirit of the revolutions of 1848, revolted and made the canton a republic (1848), angering the major powers, which in the London Protocol (1852) acknowledged the rights of Prussia's King Frederick William IV (1795-1861) but advised him not to take power unless they concurred. Nonetheless, Frederick William encouraged Neuchatels's royalist aristocrats to attempt a doup d'etat there in 1856; it failed, and 530 of the aristocrats were arrested. Neuchatel refused to release them, and Prussia prepared for war. The Swiss armed too, but action was delayed while diplomatic endeavors were made by French emperor Napoleon III (1803-73). When France announced support for Neuchatel and Britain backed France, Frederick William accepted a face-saving suggestion: he would retain for life the title prince of Neuchatel, but would renounce his sovereignty over it. Neuchatel returned to its former state as a republic and a canton, the aristocrats were released, and both armies were demobilized, much to the relief of Europe.