In the early 1930s, the US adopted an isolationist foreign policy, and three acts were passed to keep the country out of war. （1分）However, with the spread of the Second World War, the US gradually moved away from neutrality and tried to aid Britain after the fall of France.（2分）
The bombing of Pearl Harbor formally involved the US in the war.（1分）Then the US set its wartime objectives: to destroy the Axis powers and establish a new world order.（1分）Therefore, the US coordinated with Britain and formulated strategies to defeat Germany, and is also cooperated with the Soviet Union to lower its own loss while watching out for the Soviet Union’s expansion. The Guiding principles were to win the war and establish a postwar political structure.（2分）
In a word, the US adjusted its foreign policies to the changing situations for the sake of its own interests with great success.（1分）
