That's incorrect. The US is in meaningful trade confict with only a few nations:
China, Germany, France, Canada, and Mexico.
While the EU operates as a whole for the most part on these matters, the conflict is overwhelmingly with Germany's extreme trade surplus.
Canada and Mexico are about NAFTA positioning primarily.
For one example, the US runs a vast trade deficit with Vietnam. So far this year there is a five to one ratio between imports and exports with Vietnam (in favor of Vietnam). For 2017, the trade deficit with Vietnam was so large it's equal to about 20% of their entire economy. The US is not starting a trade war with Vietnam, and isn't going after Vietnam as eg the EU. Do you know why? Strategic positioning. Vietnam is a valuable future and present offset to China on offshore manufacturing; to be used to debase some of China's regional economic hegemony and to build up more regional powers that the US can work with against China in the future.
Pursuing tariffs on steel and aluminum is legitimately about US national security. It's stupid to allow those industries to erode any further given their importance. You don't want to be dependent on Japan (5%) and South Korea (11%) for steel imports in the middle of a conflict with China and or North Korea. You don't want to be asking for steel from Russia (7% of steel imports) during a conflict with Russia.
Going after Canada is primarily about positioning for the NAFTA talks. Canada does in fact have some substantial barriers in their dairy and agriculture markets. The US by contrast has nearly the lowest agriculture tariffs of any nation. The trade conflict with Canada will ultimately be trivial and will be over shortly.
All other nations are universally allowed to shelter and protect all sorts of pet domestic industries, whether it's dairy or maple syrup in Canada or energy in Mexico, or practically everything in China. The US the only nation held to an entirely different standard.