Washington, D.C. · October 2, 1939

On January 31, 1939, President Franklin D. Roosevelt held a closed-door meeting with the Senate Military Affairs Committee at the White House. Reportedly FDR made the comment that “the frontier of the United States is the Rhine,” meaning France’s eastern border with Nazi Germany. When the statement was leaked to the press, the hubbub in isolationist circles was deafening. The president denied he had made any such statement. However, one month after the outbreak of World War II in Europe in September 1939, Roosevelt was in a much stronger position vis-à-vis the isolationists and those who favored complete neutrality to define America’s eastern frontier, although the frontier was nowhere close to Europe. On this date in 1939 Roosevelt declared a region of the Atlantic adjacent to the Americas as the Pan-American Security Zone. Within the zone, which extended from 300 to 1,000 nautical miles offshore, all hostile actions by belligerent powers—meaning Germany and Italy—were forbidden. U.S naval and air patrols escorted and actively protected convoys sailing to and from Europe within this neutral zone, even broadcasting U‑boat sightings, which incurred the resentment of the German Kriegs­marine. On April 18, 1941, Roosevelt extended the Pan-American Security Zone to a point just short of the mid-Atlantic Danish dependency of Iceland, a major convoy staging area. The gap in the zone was closed when Iceland severed its relationship with the mother country and permitted the U.S. to garrison the island in July 1941.