In early 1870, the German Prince Leopold, of the Roman Catholic cadet branch Hohenzollern-Sigmaringen,[2] had been offered the vacant Spanish throne. French Emperor Napoleon III and his government voiced concern over a possible Spanish alliance with the Protestant House of Hohenzollern, which ruled the Kingdom of Prussia, protested against the offer and hinted at war. Following the protests by France, Leopold had withdrawn his acceptance on 11 July 1870, which was already considered a diplomatic defeat for Prussia. [3] The French were still not satisfied and demanded further commitments, especially a guarantee by the Prussian king that no member of any branch of his Hohenzollern family would ever be a candidate for the Spanish throne.[citation needed]