Okay, the principal belligerents in World War II were, on the Allied side, the USSR. the USA, and the UK, and on the Axis side, Germany and Japan. Fascist Italy and China (temporary alliance of KMT and Red Army forces) were second-rank powers able to give the big dogs serious resistance.
What I’m looking for here is to identify what other nations made significant contributions to the prosecution of the war, and in a broad sense what those contributions were – not the details but a summary of major contributions. To keep this a factual-answer GQ thread as opposed to an IMHO topic (“Well, Luxembourg did provide…”), “significant contribution” means either (a) active duty troops engaged in fighting, as opposed to garrisoning, proportionate to their size and in the absolute in excess of a division; (b) logistic or other ancillary support which freed up major-player troops for combat; or © guerrilla or other paramiltary activity equivalent to a Corps or better in combat effectiveness.
I know that Canadians, Aussies, and Kiwis will object that their countries did make significant contributions to the war. But that’s exactly what I’m talking about. Certainly none of them could have ever hoped to defeat a major power one-on-one, but they did provide important elements to the war effort. However, except for part of Canada’s contribution, I know little about what all that was.
Examples for (b) and © would be Norway and Yugoslavia respectively, Norway for putting the world’s 7th largest merchant marine at the service of the war effort while the homeland was under Hitler’s thumb, and Yugoslavia for the guerrilla effort that drove the German armies out of the country (admittedly with the aid of other forces fighting nearby). Finland might fall as an (a) example for the Axis, even though it wasn’t formally an ally, only de facto by force of circumstance.
So there’s the question: what countries not usually focused on in WWII histories made valuable contributions to the war for their side?