In 2008, Barack Obama campaigned as a foreign policy moderate, wary of the aggressive interventionism of the George W. Bush administration but willing to take on a leading role for America in combating particularly ominous threats. While promising to pull the remaining American forces out of Iraq, he vowed to send additional troops to Afghanistan. He said that he would collaborate with other nations to a greater extent than Bush, but at the same time served notice that he would act unilaterally when vital U.S. interests were at stake.
Barack Obama’s retrenchment policies may be unprecedented in degree, but not in kind. Other presidents have implemented pullbacks from an overseas engagement, usually after a war. These retreats have all been followed by pendulum swings back toward re-engagement. This pattern will, no doubt, hold after Obama. Historical determinism does not account for the oscillations, which are instead due to partisanship between the major political parties, domestic considerations, and ideological convictions of the commanders-in-chief as well as the need for course corrections.
Every empire or great power, no matter how interventionist it is, undergoes periods of retrenchment. For example, after the Roman emperor Trajan (r. A.D. 98-117) conquered Dacia (Romania) and fought an exhausting, at first successful but ultimately failed war in Mesopotamia (Iraq), his successor Hadrian (r. A.D. 117-138) pulled back. Hadrian accepted defeat in Mesopotamia, gave up part of Dacia, and put the empire on a defensive footing.