American never saw 9/11 coming (though perhaps we should have), but the Bush administration's response to that horrific moment was grounded philosophically in ideas and careers dating back as far in some cases as the Nixon administration.
The Vulcans, referencing the Roman god of fire, were a self-christened group of highly experienced and impressively credentialed neoconservatives within the Republican party who advocated for a more aggressive foreign policy predicated on American's unchallengeable military superiority and a moral commitment to democracy. Mann focuses on perhaps the six most influential Vulcans, all of whom, after years in government service with occasional forays into the private sector, served important and influential roles in the George W Bush administration: Vice President Dick Cheney, National Security Adviser Condoleeza Rice, Secretary of Defense Donald Rumsfeld and his second in command Paul Wolfowitz, Secretary of State Colin Powell and his second in command Richard Armitage.
Their hero was Winston Churchill, who resisted tyranny and gave a full-throated defense of democratic institutions, but their philosophical inspiration came from Leo Strauss, a political philosopher who argued against moral relativism and the accommodation of tyranny while advocating for the classical ideal of an elite group of advisers guiding national policy. An early neocon from the ranks of the Democrats, Jeane Kirkpatrick, had argued against Jimmy Carter's attempts to foster democracy in other nations, especially Iran, in her essay "Dictatorships and Double Standards," but a more aggressive and idealistic outlook on the part of the neocons gradually began to prevail over the decades.
Aside from their philosophical underpinnings, the Vulcans were strongly influenced by historical and political developments during the second half of the Twentieth Century: the need to rebuild American's military after Viet Nam and the Iranian rescue debacle, the collapse of Russia and the end of the Cold War, 9/11 and the advent of stateless terrorism, and the perceived danger of weapons of mass destruction (WMD) in unfriendly regimes that might be sympathetic to terrorist organizations.
Conservative thinking underwent a sea change from the old Nixonian approach of detente, realpolitik, maintaining a balance of power, reliance on allies, and the use of the military purely for self-defense to a new, more aggressive philosophy of unilateral, preemptive action based on American's vast military superiority, thumbnailed by the phrase "shock and awe," and moral commitment to democracy and free markets overseas. Earlier realpolitik advocates like Brent Scowcroft and James Baker provided a counterargument which never gained traction in the post-9/11 environment.
Vulcan thinking culminated in the second invasion of Iraq, a remarkable military achievement followed by a political and military fiasco during the occupation. Three Vulcan assumptions proved to be without substance: 1. Once America went into action, her allies would fall into line. 2. WMD in Iraq as casus belli. 3. The enthusiastic response of the Iraqi people to the removal of Hussein by the American liberators. The Vulcan philosophy carried them only so far. Their pursuit of unrivaled American power eventually took them beyond the will and political support of the American people, especially when their assumptions led them into the realm of nation/region building.