My dads army one the war,and also my grandads although he is in a war grave in France.People can slag off and show their contempt of proper values because of them.
So ask yourself how and why the situation they became involved in existed.
I am sure you are talking about the Great War and WW2, both of which were a product of Empire building, rampant nationalism, and overall the European countries refusing to bond collectively together in the interests of their peoples.
The European conflicts had gone on for centuries, and at the end of the Great War it was hoped that Europe could come together and avoid such conflicts again; it being the War to end all Wars. But no, due to a very complex system of individual nationalist politics at Versailles in 1919, the hopes of many were dashed, and helped to create the monster that was German National Socialism to again rack Europe, and the World, with War on a massive scale.
It was the dream of the likes of Winston Church that Europe could come together as a united body, settling differences by jaw, jaw, and not war, war. Thank goodness, coupled with the nuclear threat for all, we now have the EU with a European Government, which so far has diffused any possible slide back into nationalism, self interest, and war on a massive scale.
I lost an uncle and grandfather, along with ending up with a damaged second grandfather and father, due to those super destructive events of war, and all I now request is that we have peace at all costs, even at a price of individual nationalism.
As Thomas Hobbes rightly summed up:
"Hereby it is manifest , that during the time men live without common Power to keep them all in awe, they are in a condition which is called Warre; and such a warre, as is of every man, against every man. For WARRE , consisteth not in Battell onely, or the act of fighting; but in a tract of time, wherein the Will to contend by Battell is sufficiently known: and therefore the notion of
Time, is to be considered in the nature of Warre; as it is in the nature of Weather. For as the nature of Foul weather , lyeth not in a showre or two of rain; but in an an inclination thereto of many dayes together: So the nature of War, consisteth not in actual fighting: but in the known disposition thereto, during all the time there is no assurance to the contrary. All other time is PEACE."
Hobbes, T.
Leviathan pp. 185, 186 Penguin (1651)
Overall a warning from history you could say; May we all work together in the interests of mankind.