Neutral powers during World War II

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, Colombia, and Switzerland all helped the Allied Powers by supplying "voluntary" brigades to the United Kingdom, while Spain avoided the Allies in favor of the Axis. Ireland generally favoured the Allied side, as with the United States. The United States remained neutral until December 8, 1941, a day following the sneak attack by Japan on Pearl Harbor.

The Lateran Treaty between Italy and the Vatican, signed in 1929, required that the Pope maintain "perpetual neutrality in international relations"—making the Vatican City a neutral state.

Several countries suffered invasions in spite of 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 invaded Iceland and established an occupying force (subsequently replaced by the then-neutral United States). In the eastern Baltic, the Soviet Union invaded Lithuania, Latvia and Estonia on 14 June 1940. 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.

...
Wikipedia