By Dietrich Knauth, Blake Brittain NEW YORK (Reuters) -Five American small businesses asked a U.S. court on Tuesday to halt President Donald Trump's "Liberation Day" tariffs, arguing that he overstepped his powers by declaring a national emergency to impose across-the-board taxes on imports from nations that sell more to the United States than they buy.

Prior to President Trump's second term, there was little back and forth between the U.S. and China on tariffs. Here's what to know.