Assured of the support of Napoleon III, Count Cavour began to prepare the army of Piedmont-Sardinia for war against Austria. Napoleon III looked for diplomatic support. He approached Lord Derby (the Prime Minister of the United Kingdom) and his government; Britain was against the war, but agreed to remain neutral. Still facing strong opposition within his own government, Napoleon III offered to negotiate a diplomatic solution with the twenty-eight-year-old Emperor Franz Joseph I of Austria in the spring of 1858. The Austrians demanded the disarmament of Piedmont-Sardinia first, and sent a fleet with thirty thousand soldiers to reinforce their garrisons in Italy. Napoleon III responded on 26 January 1859 by signing a treaty of alliance with Piedmont-Sardinia. Napoleon promised to send two hundred thousand soldiers to help one hundred thousand soldiers from Piedmont-Sardinia to force the Austrians out of Northern Italy; in return, France would receive the County of Nice and Savoy provided that their populations would agree in a referendum.