It was true for other countries as well—including Belgium and the Netherlands, both of which had declared their neutrality prior to the war. Their neutral status made little impression on Adolf Hitler, who ordered his forces to invade both states as part of his attack on France in May 1940. Meanwhile, the Soviet Union invaded Lithuania, Estonia and Latvia in June. This enabled Soviet leader Joseph Stalin to expand his power, Woolner explains, and create a buffer between the USSR and Germany.
“In short, staying neutral in an ever-expanding war proved virtually impossible for these nations,” he says.
The United States, protected by two vast oceans, however, stayed neutral for more than two years despite finding ways to help the Allies. It officially entered the war after the Japanese attacked Pearl Harbor on December 7, 1941.
Author's socials

Axis Powers:
These included the nations of Germany, Italy, Japan and to a lesser degree Hungary, Bulgaria and Finland.
Allied Powers:
Prominent members included Great Britain, the United States, France, the Soviet Union and China, with support from Canada, Australia, Poland and Yugoslavia.
Axis-Supporting Nations:
Countries such as Romania, Spain, Portugal, Turkey, Sweden, Slovakia and Croatia provided some level of material, territorial or troop support to Axis powers.
Allied-Supporting Nations:
In 1942, 26 countries throughout Latin America, Africa and Asia pledged their support to fight Germany; that number increased to 47 nations by 1945.
Neutral Countries:
Many nations claimed to be neutral during the war, but continued commercial and military activities with either–or both–Allied and Axis powers.
Complex Alliances:
Throughout World War II, there were shifting pacts, agreements and treaties between nations; Italy, for example, sided with Germany until 1943, when it joined the Allied forces.
Countries That Claimed Neutrality Throughout the War
Only 14 countries remained officially neutral throughout the entire war. They included Sweden, Switzerland, Spain, Portugal, Ireland, Turkey, Yemen, Saudi Arabia and Afghanistan as well as the microstates of Andorra, Monaco, Liechtenstein, San Marino and Vatican City.
But even those states that managed to stay out of the war, such as Sweden and Switzerland, found their ability to maintain strict neutrality hampered by the intensity of the conflict, Woolner says. The result, he adds, is “they played a somewhat ambiguous—and still controversial—role in the war.”
A seminal 1998 U.S. State Department report helped dispel the myth that there was any standard form of neutrality, finding that the neutral countries continued trading with the Allied and Axis forces, sending troops to offer military assistance, and alloing one side or the other access to their territory.