In the summer of 2002, the Pentagon's Office of Net Assessment (ONA) published an 85-page monograph called "Military Advantage in History". Unusual for an office that is headed by Andrew Marshall, the Pentagon's "futurist in chief," the study looks back to the past—way back. It examines four empires, or "pivotal hegemonic powers in history," to draw lessons about how the United States "should think about maintaining military advantage in the 21st century." Though unclassified, the study was held close to the vest; a stamp on the cover limits its dissemination without permission. Mother Jones obtained it only through a Freedom of Information Act request. Though the report is far from revelatory, it provides a window into a mindset that unselfconsciously envisions the United States as the successor to some of history's most powerful empires.