At the start of World War II in 1939, the Portuguese Government announced on 1 September that the 550-year-old Anglo-Portuguese Alliance remained intact, but since the British did not seek Portuguese assistance, Portugal was free to remain neutral in the war and would do so. In an aide-mémoire of 5 September 1939, the British Government confirmed the understanding. As Adolf Hitler's occupation swept across Europe, neutral Portugal became one of Europe's last escape routes. Portugal was able to maintain its neutrality until 1944, when a military agreement was signed to give the United States permission to establish a military base in Santa Maria in the Azores and thus its status changed to non-belligerent in favor of the Allies.