A major summer reading discovery this year was Jeffrey Meiser's Power and Restraint: The Rise of the United States, 1898-1941. I highly recommend it. Meiser surveys 34 cases when U.S. officials considered political-military interventions abroad and shows how many times domestic structural restraints -- especially congressional opposition or public opinion -- limited or prevented expansionist policies.
Most of the cases involve Latin America,where my own background knowledge was sketchy at best. Meiser's basic narrative is that, after an outburst of territorial expansion int he wake of the war with Spain in 1898, the United States was more restrained in subsequent years of Republican presidencies. Although Woodrow Wilson did intervene several times in Mexico and elsewhere, Meiser argues that he acted with significant restraint both because of his own anti-imperialist ideology and because of public opposition.
In the aftermath of World War I, even formerly expansionist Republicans acted with restraint. And Franklin Roosevelt enshrined the noninterventionist Good Neighbor policy as the basis for regional actions.
I have long believed that Congress can have a major shaping force over foreign policy,for both good and bad, so I'm glad Meiser provided additional evidence of how this power operated in the early 20th century.