WASHINGTON--Winston Churchill predicted World War I two years before it broke out, Library of Congress scholars discovered in a newly unearthed collection of the British prime minister's letters. The letters to Churchill's cousin, the Duke of Marlborough, have not been seen in decades, Librarian of Congress James H. Billington said. As first lord of the Admiralty in 1912, Churchill updated his cousin on the war between Turkey and an alliance of Balkan states. Churchill took a stand against the Turks. "But the European situation is far from safe and anything might happen," he wrote. "It only needs a little ill...