I visited the Gettysburg National Park last summer to see where my great great grandfather fought for the Massachusetts 8th Regiment. Most of the same blunders made in 1863 were perpetuated in WWI, but to an even larger extent. WWI was a stalemate over a few miles of front for years; at least the American Civil War had more mobility.
If you study psychopathy, quickly you come to realize the WWII was started and fought by the Axis powers for psychopathic motives more than anything else. Certainly any war can be justified by revisionist historians as being fought for economic reasons, but the reality is that empires and colonies and greed have existed since before Greco-Roman times but have not always resulted in war. Psychopathic behavior (which is evil by definition) was exhibited by Hitler, Mussolini, Tojo, Stalin, and later by Mao and the North Koreans. Whenever genocide shows up in war, it's the result of psychopathics in control. During the 20th century, over 100 million people died at the hands of the twisted minds of psychopaths. During WWII, the Allies fought a "Good War" against some of the most evil minds to team up in history. Certainly there were economics and empires, but during WWII Franklin Roosevelt pretty much made Churchill give up on a colonial strategy in return for US war support.