Final answer:
The Dual Alliance marked a change in foreign policy for the United States, which historically avoided foreign alliances. This shift occurred post-World War II when the U.S. moved from isolation to active engagement due to the weakening of traditional European powers.
Step-by-step explanation:
The Dual Alliance represented a significant shift in foreign policy, especially for countries like the United States which had a long history of avoiding foreign entanglements that might necessitate sending troops abroad. This policy changed post-World War II as the United States recognized that in the face of weakened traditional powers like Great Britain and France, it would have to become more actively engaged in international affairs. This marked a departure from its earlier stance of relative isolation to one of active foreign engagement.