President Donald Trump has started the trade war anew with fresh announcements of steel and aluminum tariffs that prompted swift threats of retaliation from key allies.

Canadian Prime Minister Justin Trudeau expressed his disappointment with the decision, taken as the US, Canada, and Mexico are attempting to renegotiate the North America Free-Trade Agreement.

"It’s ramping up the whole trade war tone and it’s unnecessary particularly with our allies," Dec Mullarkey, managing director of investment research at Sun Life Investment Management, told Business Insider.

Just ten days after Treasury Secretary Steven Mnuchin said that the US trade war against major commercial partners was on hold, President Donald Trump unveiled a new round of tariffs targeting some of America’s closest allies.

US stocks took a dive after Trump, having previously vacillated on the issue, announced Mexico, Canada, and European Union member countries would be hit with new tariffs on steel and aluminum. The move sparked immediate threats of retaliation from those nations, renewing fears of a damaging global trade war.

"It doesn’t make any sense," Dec Mullarkey, managing director of investment research at Sun Life Investment Management, told Business Insider.

“The current administration is very transactional and visceral but our allies are very strategic and deliberate. It comes just as there had been quite a bit of progress on NAFTA" deliberations, Mullarkey said.

Canadian Prime Minister Justin Trudeau certainly minced no words.

While market participants hope Trump is blustering and may not actually follow through with many of the harshest proposed measures, the increasing uncertainty is starting to hang over the global economy.

"It’s ramping up the whole trade war tone and it’s unnecessary particularly with our allies," Mullarkey said. The bigger concern, according to Mullarkey, is that threats to curb auto imports from countries like Germany could become policy at any moment, threatening a huge sector of the global economy with potentially wide supply chain ramifications.

China, on the other, hand, is taking the long road with Trump. They see it as in their interest to appear to make some concessions to the US president, all the while flexing their global muscle as the world’s second largest economy, and increasingly, a chief champion of open trade, a historic role reversal.

"They will give Trump wins but they are looking at this through the China 2025 lens. They want to become a powerhouse in artificial intelligence, technology, automated vehicles. They’re very serious about building a coalition with Europe and others," Mullarkey said.

That risks leaving the United States behind.