The single largest obstacle to large-scale international warfare has been international trade. Global trade has made it massively expensive and consequential to declare war on your neighbors - because it disrupts the steady inflow of money. The more trading partners a nation has, the less likely it is to go to war with any of them. It's why the US and China avoid direct conflict with each other - the cost of going to war is too high, both short-term and long-term.

If international trade breaks down, a lot of the incentives for peace go with it. National economies will struggle internally, and some of those nations will look outward for ways to enrich themselves.

Either Trump is an idiot and is risking the entire world for short-term profit (which I wouldn't put past him), or he's intentionally eroding the stability of international trade because he wants conflict.