Since U.S. President Donald Trump first threatened to place massive tariffs on Canadian goods, the country has been embroiled in a whirlwind back and forth with its biggest trading partner. Here's a quick look at how tariffs are set under normal circumstances.

President Donald Trump has promised a massive escalation of his global trade war on April 2, when far-reaching tariffs will be imposed on nations around the world

It started with tariffs, but the trade war is quickly escalating beyond import taxes into a broader tit-for-tat battle.