The neutral powers were countries that remained neutral during World War II. Some of these countries had large colonies abroad or had great economic power. Spain had just been through its civil war, which ended on 1 April 1939 (five months prior to the invasion of Poland)—a war that involved several countries that subsequently participated in World War II.
During World War II, the neutral powers took no official side, hoping to avoid attack. However, Portugal, Sweden, and Switzerland all helped the Allies by supplying "voluntary" brigades to the United Kingdom, while Spain avoided the Allies in favor of the Axis, supplying them with its own voluntary brigade, the Blue Division. Ireland generally favoured the Allied side, as with the United States. The United States remained officially neutral until 8 December 1941, a day following the attack by Japan on Pearl Harbor.
The Lateran Treaty between Italy and the Holy See, signed in 1929, required that the Pope maintain "perpetual neutrality in international relations". Accordingly, Vatican City was officially neutral throughout the war.
Several countries suffered invasions despite their efforts to be neutral. These included Nazi Germany's invasion of Denmark and Norway on 9 April 1940—then Belgium, the Netherlands, and Luxembourg on 10 May 1940. On the same day, 10 May 1940, the British, having already invaded the Faroe Islands in April, invaded Iceland and established an occupying force (subsequently replaced by the then-neutral United States). The Soviet Union invaded Lithuania on 15 June 1940 and Latvia and Estonia on 17 June. In the Balkans, the Italo-Greek War began on 28 October 1940 and Yugoslavia was invaded in April 1941. Iran was also attacked and occupied by Britain and the Soviet Union in August 1941 and later declared war on Nazi Germany.
See also the histories of Afghanistan, Andorra, Guatemala, Liechtenstein, Saudi Arabia and Yemen during this period.
By country
Europe
Estonia, Latvia, and Lithuania
, , and – The Baltic states of Estonia, Latvia, and Lithuania, jointly declared their neutrality on 18 November 1938, in Riga, at the Conference of Baltic Foreign Ministers with their respective parliaments passing neutrality laws later that year. Despite that, all of them were occupied twice by the Soviet Union and once by Nazi Germany.
Iceland
– Occupied by Allied forces from May 1940.
Ireland
– The policy of Irish neutrality during World War II was adopted by the Oireachtas (Irish Parliament) at the instigation of Éamon de Valera, the Taoiseach (head of government) upon the outbreak of hostilities in Europe. It was maintained throughout the conflict, in spite of several German air raids and attacks on Ireland's shipping fleet by the Axis. De Valera refrained from joining either side, although he generally favored and aided the Allied powers by allowing access to their naval repair yards.
Portugal
– Portugal was officially neutral during World War II. However, it maintained a close relationship with the UK, due to the alliance it had for the last six hundred years, which is the longest lasting military alliance in history. The Estado Novo sought neutrality in order to keep Spain neutral and prevent it from joining the Axis. Portugal allowed the United States to use a secret military base at Santa Maria Airport in the Azores through a military agreement signed on 28 November 1944. This violated its neutrality and rendered Portugal as a non-belligerent on the Allied side.
Colonies of Portugal: Angola Cape Verde Portuguese Guinea Portuguese India Macau Mozambique São Tomé and Príncipe Portuguese Timor (Occupied by Japan from 1942 to 1945)
Spain
– Spain initially held to formal neutrality, but when Italy entered the war in June 1940, Francisco Franco changed Spain's status to that of "non-belligerent" and proceeded to occupy Tangiers. From June 1940 until February 1941, the Francoist regime was greatly tempted by interventionism; a prominent Germanophile, Foreign Minister Ramón Serrano Suñer was highly influential in the government. However, meetings with German officials, including the Hendaye meeting between Franco and Hitler on 23 October 1940, did not bring formal entry of Spain into the war.
Operation Barbarossa shifted the main theater of war away from the Mediterranean, lessening Spain's interest in intervention. The less-relevant Serrano Suñer was still able to create the Blue Division, made up of Spanish volunteers to fight for the Axis. With the conflict decidedly turning in favor of the Allies, Franco returned the status of Spain to one of "vigilant neutrality" on 1 October 1943.