It gets tricky when it comes to the fundamental sources of both world wars.

"Exploitable real estate was not the mightiest driver of global mayhem, whatever the rhetoric. In support of his thesis, Overy can invoke the Kaiser’s imperialist grandstanding and the Brest-Litovsk Treaty of 1918, when the German diktat chopped off the Baltics and Ukraine from the Soviet Union.

Land über alles? Note that war aims expand after initial victories; they should not be equated with the underlying cause of bloodshed. Greed has to carry too much explanatory weight, though Overy insists that in the 1930s, “the critical factor for Japan, Italy and Germany was territory.” Looking at the two world wars together, theorists of international politics stress more systemic factors, which outlive classical imperialism. The strongest is an old acquaintance. 

Thucydides argued 2,500 years ago that “the real reason” for the Peloponnesian War “was the rise of Athens to greatness and the fear it caused in Sparta.” 

And thus in Europe in the run-up to the second Thirty Years’ War, 1914-45, there was a muscular upstart in the game: rapidly growing Germany. And with wealth comes ambition; nations turn rich, then rowdy — as did the United States circa 1900. The Spanish-American War was for pre-eminence, not plantations. McKinley held on to the Philippines to pre-empt America’s great-power rivals in the Pacific.

Power politics is not the same as imperial greed. When the balance tilts, states worry about survival. The war in the Pacific was not about real estate as such. The true culprit was unchecked Japanese power, culminating in the assault on Pearl Harbor. California next? Nor did France and Britain declare war on the Third Reich for the sake of their overseas properties. The motor was existential angst after Hitler’s attack on Poland as prelude to the conquest of Europe.

So, “imperial wars” should not be conflated with “systemic wars,” which are fought for balance of power and the survival of nations. 

The United States did not wade into World War I to safeguard Samoa. The mortal threat was the Kaiser’s U-boat warfare directed against America’s Atlantic lifeline. Did the Soviets grab Eastern Europe after 1945 for its wheat fields? No. They wanted to bottle up American power in Western Europe. 

America’s postwar “empire,” its far-flung (and costly) alliance system, was not intended to enrich the United States, but to stave off the Soviets. 

The central game is usually about strategic competition, not arable land and cheap labor, though governments often do invoke riches to mobilize nations for war."