However, the Ottomans began to face many challenges. The failure to conquer the Safavid Empire forced it to keep forces in the east, while the expansion of the Russian Empire put pressure on the Black Sea territories. Meanwhile, Western powers began to overtake their maritime capabilities, with the Battle of Lepanto (1571) being a turning point. In 1683, the Battle of Vienna halted an Ottoman invasion again, with the Christian Holy League driving the Empire back into the Balkans. Despite the Venetian reconquest of Morea (Peloponnese) in the 1680s and it was recovered in 1715, while the island of Corfu under Venetian rule remained the only Greek island not conquered by the Ottomans. The Ottoman Empire still remained the largest power in the Mediterranean and the Middle East.