In order to provide a "hitchhiker's guide" to America's Foreign Policy, Mead constructs a four node framework which articulates his major schools - a good summary paragraph from the introduction [p xvii]:
Americans through the centuries seem to have had four basic ways of looking at foreign policy, which have reflected contrasting and sometimes complementary ways of looking at domestic policy as well. Hamiltonians regard a strong alliance between the national government and big business as the key to both domestic stability and to effective action abroad, and they have long focused on the nation's need to be integrated into the global economy on favorable terms. Wilsonians believe that the United States has both a moral obligation and an important national interest in spreading American democratic and social values throughout the world creating a peaceful international community that accepts the rule of law. Jeffersonians hold that American foreign policy should be less concerned about spreading democracy abroad than about safeguarding it at home; they have historically been skeptical about the Hamiltonian and Wilsonian policies that involve the United States with unsavory allies abroad or that increase the risks of war. Finally, a large populist school I call Jacksonian believes that the most important goal of the U.S. government in both foreign and domestic policy should be the physical security and the economic well-being for the American people.
So basically, Hamiltonians = Traders, Wilsonians = UN, Jeffersonians = Libertarians, Jacksonians = Hawks.
He does an AWESOME job of credibly explaining all 4 schools in a manner which is both equally complementary and critical and shows no outward sign of bias. (he "comes out" later in the book and states that his own biases are towards the Jeffersonian school). Membership in a school is by no means exclusive (one can be a Hamiltonian about China, for example, but a Jacksonian towards the Middle East) and, Mead elegantly demonstrates, the plurality of voices are actually able to feed and buttress each other and achieve goals far better than any one school alone - the Wilsonian / Jacksonian Good Cop / Bad Cop routine is probably the easiest to imagine.