"We canceled the TPP, the Trans-Pacific Partnership," he said. "We're pulling our troops out of South Korea eventually."
"The signal is being sent [to the world] ... that you're on your own," Cohen said on "Closing Bell" Tuesday.
The military exercises are an annual event held in South Korea, in which the U.S. has historically participated, that both nations say are intended to deter North Korea.
The reclusive nation to the north, meanwhile, has previously expressed disapproval of the exercises, saying they are a preparation for war.
But Trump later said in a press conference that he would end what he referred to as the "war games" not as a concession but because they are too expensive.
"It will save us a tremendous amount of money," Trump said. "The amount of money we spend on them is incredible."
Cohen said the exercises are expensive, but pointed out that it's more expensive to be ill-prepared for military conflict or to lose a war.
"We lost thousands in battle in the Korean conflict because we were ill-prepared and not well-trained or well-equipped," he said.
"Yes, it's very expensive to be in shape, to be ready to defend our country and our allies in the region," Cohen said. "To point out how expensive it is misses the point of what strategic deterrence is and how it protects U.S. interests as well as those of South Korea."
Meanwhile, representatives from South Korea were conspicuously absent from the summit.
John Rutledge, chief investment officer at Safanad, a financial firm, said the summit was a complete slap in the face to South Korea "because the president of South Korea was not in the room when they did this."