President Obama sent 1,000 Air Force Academy cadets into active duty Wednesday by laying out his vision for a postwar America in which the United States leads beyond the battlefield and by defiantly challenging his critics’ notion of waning American influence. In a commencement address to the graduating service members, Obama hailed a milestone moment: The Class of 2012 is the first in nearly a decade that is entering active service with no American troops fighting in Iraq and the first that can envision an end to the Afghanistan war.