Eugene returned to Vienna from his recent victory at Belgrade (before the conclusion of the Turkish war) determined to prevent an escalation of the conflict, complaining that, "two wars cannot be waged with one army"; only reluctantly did the Prince release some troops from the Balkans for the Italian campaign. Rejecting all diplomatic overtures Philip V unleashed another assault in June 1718, this time against Savoyard Sicily as a preliminary to attacking the Italian mainland. Realising that only the British fleet could prevent further Spanish landings, and that pro-Spanish groups in France might push the regent, Duke of Orléans, into war against Austria, Charles VI had no option but to sign the Quadruple Alliance on 2 August 1718, and formally renounce his claim to Spain. Despite the Spanish fleet's destruction off Cape Passaro, Philip V and Elisabeth remained resolute, and rejected the treaty.