If protectionism is good, then why did the world move away from it when it did? I ask this question in good faith: global trade definitely has its downsides, b

If protectionism is good, then why did the world move away from it when it did? I ask this question in good faith: global trade definitely has its downsides, but one positive aspect it has is that reduces the probability of armed conflict taking place between countries trading with one another. All else being equal, waging war on a customer deprives one of their business, and waging war on a supplier deprives one of that source of supplies. To your point, cultivating your in-house engineers on a given project means that those engineers are tied up in that endeavour as opposed to working on something that has a higher return on investment.