Final answer:
The correct answer is option c. The U.S. began incorporating a liberal internationalist approach to foreign policy during and after World War I and World War II, primarily under the influence of President Woodrow Wilson and later due to the necessity of active engagement during WWII.
Step-by-step explanation:
The period that prompted the U.S. to begin incorporating policy measures that reflected a liberal internationalist approach to foreign policy was World War I and World War II. President Woodrow Wilson's foreign policy initially aimed to reduce American involvement abroad and to act on moral imperatives.
However, the moral implications of Germany's war tactics in WWI, the need to protect American trade interests, and ultimately the shared democratic values led to Wilson advocating for the creation of the League of Nations, thus ushering the United States into an era of liberal internationalism.
After WWI, isolationist tendencies prevailed until the rise of totalitarian regimes and aggression from the Axis powers in WWII necessitated a more engaged U.S. approach. The subsequent creation of the United Nations and America’s role in constructing a new global order further cemented the shift towards liberal internationalism.