Does anyone doubt this? Consider the pressures.

Global warming, with disruption of fresh water resources, food production, population centers. There will be wars.

Continuing poverty, with the wealthy getting wealthier and the poorer poorer. There will be revolutions.

More expensive energy, with wealthier nations leaving little for the poorer nations. There will be wars. (The US was willing to go to war over Iraq's oil even this early in the century. If China had contested that instead of waiting and outbidding the US later, it could have been uglier.)

Wars are expensive, wasteful, and consume vast amounts of energy and other resources. Wars fought over scarce resources seem especially foolish, but that's the way it's been since Man could sharpen a stick.