What it's "really" about is something that future historians can try to figure out, but in situ it's almost impossible to tell.

We can list all kinds of factors that came together when the conflict started or which factors are around while the conflict keeps going for a long time. What it's "about"? That kind of answer only really exists in games like Civilization where the answer is "because a player wanted X" or "the PC faction AI decided that the value of war exceeded the cost" ... the real world doesn't have as neat an answer.

Beware those who are sure about the "real reason": they are either ignorant of the complexities of societies and wars or they have an agenda.

And even those future historians won't be able to pinpoint a single reason for all of this (or most other wars), because it's almost always multiple factors acting together.

Imagine for a second a war that looks like it's "clearly about the aggressor getting land/resources": that might be the main reason, but maybe historical and religious factors made the war easier to "get going" for those who don't actually care about that (or the other way around: someone powerful want's to wage a religious war, but it's easier to convince the military to fight for the resources ...).