The prolonged conflict exhausted the economy of the Republic, which relied on the lucrative trade with the Ottoman Empire. By the 1660s, despite increased aid from other Christian nations, war-weariness had set in. The Ottomans on the other hand, having managed to sustain their forces on Crete and reinvigorated under the capable leadership of the Köprülü family, sent a final great expedition in 1666 under the direct supervision of the Grand Vizier. This began the final and bloodiest stage of the Siege of Candia, which lasted for more than two years. It ended with the negotiated surrender of the fortress, sealing the fate of the island and ending the war in an Ottoman victory. In the final peace treaty, Venice retained a few isolated island fortresses off Crete, and made some territorial gains in Dalmatia. The Venetian desire for a "revanche" would lead, barely 15 years later, to a renewed war, from which Venice would emerge victorious. Crete, however, would remain under Ottoman control until 1897, when it became an autonomous state; it was finally united with Greece in 1913.