It's useful, but not a prerequisite.
With reference to slavery, it had been abolished in Britain on the grounds that one man could not own another - bodily or spiritually - although it exists amongst migrants from the Third World (people traffickers have a hold on those they bring in by threatening to expose their 'clients' to the authorities).
Going back in time there was a jingoistic support for fighting 'the Hun' that had its basis in the rivalry between 'Kaiser Bill' (Wilhelm) and his uncle Edward VII. The Kaiser fostered the support of Tsar Nicholas by denigrating his British relatives, and entered the dispute between Kaiser Franz Josef of Austria and Serbia over the assassination of his nephew and successor Franz Ferdinand in Sarajevo... It was a game of dominoes between the royal families and governments of Europe that Woodrow Wilson tried to steer clear of. It was the sinking by a German U-Boat of the Lusitania with US citizens aboard that finally brought the USA into WWI in 1917. The Kaiser had ordered the reversal of normal practice by submarines, of surfacing to warn captains of merchant or other non-military vessels.
Beneath the surface he suffered from an inferiority complex about his withered right hand - the result of botched birth procedure by obstetricians in Berlin. Why a complex? Over centuries it was literally beaten into left-handed children in most European countries including Germany and Austria that they were mentally backward, and that they should use 'die gute hand' (the 'good hand', a hangover of centuries of Church dogma where the left hand - sinister - was the tool of the devil).
That's the root of the problem. When Hitler's forces overran Western Europe in 1940 Wilhelm, then resident over the border in the Netherlands, cheered the Fuehrer and voiced his hope that he would ascend the throne of Germany again. Hitler called him an old duffer (or words to that effect) and Wilhelm died later the same year.
As I said, it helps to know the causes by studying the men. We know Hitler had a raft of mental problems big enough to warrant a page of their own. He took them with him to the bunker in Berlin and they went up in flames with him - or whichever theory you subscribe to. As he was in the advanced stages of Parkinsons he wouldn't have lasted much longer. Eva Braun had her own problems.