Britain had entered an era of "splendid isolation", avoiding entanglements that had led it into the unhappy Crimean War in 1854–1856. It concentrated on internal industrial development and political reform, and building up its great international holdings, the British Empire, while maintaining by far the world's strongest Navy to protect its island home and its many overseas possessions. It had come dangerously close to intervening in the American Civil War in 1861–1862, and in May 1871 it signed the Treaty of Washington with the United States that put into arbitration the American claims that the lack of British neutrality had prolonged the war; arbitrators eventually awarded the United States $15 million. Russia took advantage of the Franco-Prussian war to renounce the 1856 treaty in which it had been forced to demilitarize the Black Sea. Repudiation of treaties was unacceptable to the powers, so the solution was a conference in January 1871 at London that formally abrogated key elements of the 1856 treaty and endorsed the new Russian action. Russia had always wanted control of Constantinople and the straits that connected the Black Sea to the Mediterranean and would nearly achieve that in the First World War. France had long stationed an army in Rome to protect the pope; it recalled the soldiers in 1870, and the Kingdom of Italy moved in, seized the remaining papal territories, and made Rome its capital city in 1871 ending the risorgimento. Italy was finally unified, but at the cost of alienating the pope and the Catholic community for a half century; the unstable situation was resolved in 1929 with the Lateran Treaties.