https://www.cnbc.com/2018/04/04/one-of-the-biggest-us-trade-wars-of-the-past-had-a-tragic-consequence--heres-what-happened.html
Let's take it back to the 1930s. America was turning inward with protectionist policies. The government was restricting trade with other countries. And in an effort to save U.S. factories, a couple of congressmen came up with a plan. It was formally called the Tariff Act of 1930, but it's more commonly known as the Smoot-Hawley Tariff Act.
The plan faced a lot of opposition, but it ultimately became law. The act raised tariffs on American imports to nearly record levels. But instead of reviving the economy, it actually exacerbated the Great Depression.
Nations across the world were striking each other with tit-for-tit tariffs. European countries put a tax on American goods, which slowed trade between the U.S. and Europe. That made it harder for the U.S. to crawl out of its economic slump.
Nationalist rhetoric was heating up, with countries blaming others for their struggles. All of that eventually escalated, turning a trade war into a real war when World War II began.
That's why after the war ended, nations formed the World Trade Organization to regulate international trade, in the hopes that nothing like the global trade war of the 1930s would ever happen again.