People fight because their country asks them to. If it was about ideology, it would be utterly random what the nationalities of the soldiers on each side are.

Questions probably needs better definitions - armed forced fight first for their squad/team. What does "believe" mean? Accept? How many soldiers in any country "believe" in their national ideology? (Most countries have at least two political parties with different interpretations of the ideology). Is "belief" necessary? Is it even important? particularly when a country is at war, it is difficult to distinguish between, "I would lay my life down to protect this ideology" vs "I would rather fight than surrendur to whatever the other side would do to me/my squad/my family/etc."

Further complicated by the German Stab in the back myth; German soldiers had a reasonable expectation that the Allies would not treat them fairly/well. Possible to serve an ideology that you don't like because the alternative (punitive reparations) are worse. Fascinating question, but difficult to answer.

Also, it is easier to believe in your government / ideology when you are winning than when you are losing. What part of the ideology did tank driver reject? That he was part of the master race? Or only that Hitler was a providential leader that would lead Germany to a total victory? Was he opposed to the treatment of Jews and Slavs or only to being in the losing side?

@T.E.D. to be fair WWII had a significant ideological facet, with people in many conquered countries willing to support the invaders at least as a lesser evil against internal opposition.

Final thought - Once you're in the service, belief is irrelevant; desertion and sedition are heavily punished, and most people "believe" in avoiding death and dishonor.

@T.E.D.: Many don't have much choice in the matter. They get drafted.

@jamesqf - Exactly

@SteveBird While unbiased surveys during the war are unrealistic, one can have information from ex-soldiers after the war. I don't know if this has been done systematically but, as an anecdote, one member of my family was a soldier and said he did believe the ideology and only realised after the war how wrong it was. Also there are personal diaries and such. What's hard for us to understand is how little information/knowledge about the world and reliable news sources people actually had.

@StephanMatthiesen But after the war people who fought for the Nazis had motivation to lie about the level of their support. In that case the bias would run in the opposite direction, but it would be bias all the same.

Hi Abraham, this question might help to address some of these queries. history.stackexchange.com/questions/35690/… The short answer is that a tiny number of Germans (soldiers or otherwise) opposed Hitler all the way through, some supported him all the way through, and the vast majority supported him as long as he was winning, and opposed him when he was losing. Given the appalling consequences of living in a defeated country, the latter position is understandable, to some extent.

Germans fought for Hitler for the same reason the French fought for Napoleon; even after the second world war, they still fought for Algeria; the Weimar Republic was a new (and foreign) concept, which, rather unsurprisingly, came to a screeching halt, the people being accustomed to authoritarian (rather than democratic) and expansionist or imperialist rule (as opposed to self-governing nation-states).

@JohnColeman Yes, but it's more complicated. Info comes not just from what soldiers said immediately after the war but all through the 20th cent, also family stories (I heard bits from my family the 80s), and you have to consider things like the generational conflicts of the 1960s when the next generation dug out their fathers' stories. All have to be seen with the usual caveats of historical sources. I just wanted to oppose the simplistic view that you can't know what people thought because they weren't asked. There are loads of stories.

@StephanMatthiesen Good points.

I haven't read the whole thread but the question seems answerable: On D-Day forced conscripts from eastern europe stationed near the beach often did the good and smart thing - shot their german officers and surrendered. German soldiers fought a long hard battle. AFAIK in the invasion of sicily, italian soldiers more readily surrendered than german ones (which can be checked by looking a captured/killed). Basically you can look at how many german soldiers surrendered vs. fought on in the latter stages of the war and get a good picture. Another source would be letters and memoirs of soldiers.

Other possible sources: what German prisoners of war said, during formal interrogation or informal conversations with or overheard by their guards. In Britain German POWs were assigned to different prisoner of war camps depending on how pro- or anti- Nazi they appeared to be when questioned. Questioning of prisoners might also seek to discover the strength of their army's morale. Also those neutral countries who maintained embassies in or traded with Germany may have been able to observe German morale.

I don't know why this question is 'closed' as it seems reasonable and important. Of course, as with most questions about history, evidence may be incomplete and we have to consider whether sources may be biased, but those are normal problems in study of history.