It's funny how History changes based on where you learn it. That's the interesting thing about history, unless you were there you are simply taking someone elses version of the events. And even then if you were there it's your version, through your eyes it could be completely different through someone elses.
In the US we are taught that the world could not survive without our heroic efforts. That Hitler was the worst and what he did to the Jews was inhuman (and it was), what we don't really touch on is the concentration camps we had for the Japanese, this goes largely ignored in our history books. In North Korea they are taught that they won the war. In Britain you're obviously taught that you would have defeated Germany with or without our help.
As such I try to base my theories (that's all they are theories) on logic. Most of the time I find that what makes the most sense is conflict in resources. Oil and Iraq is an obvious example. But even if you look at Isreal vs. Palestine the media preaches that it's a battle over sacred holy lands, they never mention how crucial water is as a resource there and how the area of Land being fought over resides over a huge water table. Similarly many of these conflicts are deemed important for humanitarian reasons, the Ukrain and Russian conflict and why the world should get involved. But look at Syria, that country is still a mess 1700 deaths in the last 2 weeks, but the media isn't covering it. Why is that?
TLDR; History is a Bill as are the media portrayed reasons countries get involved in conflicts.