Later in the year, to strengthen the Treaty of Utrecht, Britain, France, and Austria contemplated ceding Sicily to Emperor Charles VI. This arrangement displeased Spain, which wanted to regain Sicily. In August 1717 Philip attacked Austria, which was heavily engaged in the Austro-Turkish War of 1716-18. Spain invaded Sardinia,  which was subdued by November 1717. The initial Austrian reaction to this invasion was limited, as the Austrian Supreme Commander, Prince Eugene of Savoy, wanted to avoid a major war in Italy as long as the conflict in the Balkans continued, soaking up Austrian troops and resources. Finally, on 21 July 1718, the Treaty of Passarowitz ended the war with the Ottoman Empire. On 2 August, the Emperor joined the Triple Alliance, which became the Quadruple Alliance for which the war is named.. How many countries conspired to strengthen the Treaty of Utrecht?