The Trump administration's global trade war is spreading to more countries instead of wrapping up, according to Katie Nixon, chief investment officer of Northern Trust Wealth Management.

Even though Wall Street is growing increasingly optimistic — especially after Trump and Chinese President Xi Jinping agreed to trade-war ceasefire over the weekend — the US president has recently ramped up his rhetoric against Vietnam, Japan, Mexico and India.

Nixon says that the widening dispute means businesses are facing even more uncertainty, and as that continues, it will have more of an effect on their spending and growth.

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Just as the world starts hoping the trade war between the US and China is calming down, it might actually be spreading.

The world's two biggest economic powers may have announced a ceasefire in the dispute over the weekend, but some experts argue the Trump administration's trade-policy conflicts involve more countries than ever.

"Trump has been saber rattling with Europe over trade, (and) Japan, India," Katie Nixon, chief investment officer of Northern Trust Wealth Management, told Business Insider in an interview. "Trade is going to continue to be sort of this whack a mole game."

She continued: "I wish we could move past it, but I don't think we will."

While investors are likely to applaud any positive developments between the US and China, that might set the stage for disappointment as new fights pop up elsewhere.

It makes sense that the US-China trade war has drawn the most focus: The two countries have the world's largest trade relationship, with hundreds of billions' worth of goods and services going back and forth. But beyond the dollar value of individual tariffs, the conflicts and their uncertain resolution create trouble for businesses.

And the more countries are involved, the more businesses are affected.

"If you're in a global market it's very hard to make long lived decisions right now," Nixon said. "That heightened level of uncertainty can have a negative feedback loop through the real economy as companies decide to sit on their hands while people work out the policies."

That can have quick effects on global economic growth as businesses try to find their bearings.

The trade disputes and accompanying uncertainty have spread quickly. At the end of May, Trump announced a dramatically escalating series of tariffs on Mexican goods that had investors panicking. A week later he said he they were "indefinitely suspended."

Just this week Trump threatened to put tariffs on goods from Vietnam, a country that has benefited from the trade war as some companies have shifted manufacturing away from China. Earlier this month he ended trade privileges for India, which put some tariffs on US imports.

He's said there are problems in US-Japan trade as well. And taxes on European goods might be coming. Last month, potential tariffs on cars were delayed, but that issue could come back in focus, too.

Experts agree that progress between the two sides might be much slower than the market is expecting.

"Nothing has changed that would suggest that China and the US will reach a common ground; if anything, both sides are digging their heels in," Kristina Hooper, chief global market strategist for Invesco, said in a recent client note. "It is highly unlikely that a says she thinks progress between the two sides is going to be much tougher and slower than the market is expecting.

Nixon agrees, suggesting there could be repeats of the May blowup that sent stocks sharply lower.

"What we have is this history of two steps forward, one step back," she said, adding that as the 2020 presidential election draws nearer, China might change its negotiating tactics in the hope of getting a different deal from Trump's successor.

Nixon thinks that would make the dispute last even longer and would continue to affect company earnings.

"You've already got companies moving around their supply chains, reconfiguring their supply chains, which is very distracting and it can be expensive," she said. "Companies are already recognizing that this is going to be a long lasting issue."