President Obama rallied world leaders Friday to confront the growing threat of the Islamic State and defended his administration’s aggressive use of airstrikes against terrorist groups outside of declared war zones. Obama said that in recent weeks the U.S. military has stepped up attacks on terrorist training camps that have killed scores of suspected fighters aligned with al-Qaeda or the Islamic State in Libya, Yemen and Somalia. The summit’s ambition was tempered by the absence of Russia. Russian President Vladimir Putin boycotted the gathering amid tensions with the United States and other Western nations over Russia’s annexation of Crimea in Ukraine and its support of Syrian President Bashar al-Assad.