On 15 August 1971, though the Shah of Iran was claiming historical sovereignty over Bahrain, he accepted a referendum held by the United Nations and eventually Bahrain declared independence and signed a new treaty of friendship with the United Kingdom. Bahrain joined the United Nations and the Arab League later in the year. The oil boom of the 1970s benefited Bahrain greatly, although the subsequent downturn hurt the economy. The country had already begun diversification of its economy and benefited further from the Lebanese Civil War in the 1970s and 1980s, when Bahrain replaced Beirut as the Middle East's financial hub after Lebanon's large banking sector was driven out of the country by the war.