In the world's current economic situation it pretty much is mostly all about the U.S. and the dollar.
Most of the global trade is conducted with the dollar and he can mess up other currencies in a similar way.
Why did not previous Presidents think of it and opted for traditional war? This trade war is more safer for Americans.
>why didn't previous presidents think of it
They probably did, but were likely smart enough to figure out that a trade war with the world will trigger a backlash that the US won't be able to handle. The world will seek an alternative to the US dollar, and I think it will happen very soon if Trump continues doing what he does.
US Chamber of Commerce after Turkey imposition of the tariff on US goods.
https://www.cnbc.com/video/2018/07/03/us-chamber-of-commerce...