Interesting point - I did a quick mental exercise to see if I could come up with at least ONE war who's origin could not be due to a "corrupt dictatorship trying to hold to power" and the only one that I could possibly say is an exception, is the Vietnam War, whose origin I trace to a colonial power trying to retain that which it had effectively lost...
...which was still affected by a few would-be dictator military leaders, with their own agendas; more so by some who were economic dictators in their own little corners, benefittiing from the war's continuation...
It can be noted that these things don't directly refute your statement, however.