In July, the United States and South Korea announced the deployment of a Terminal High Altitude Area Defense (THAAD) battery in Seongju County, in the country’s south. South Korea’s deputy national defense minister, Yoo Jeh Seung, said that the THAAD deployment will “protect one-half to two-thirds of the entirety of our citizens from North Korean nuclear and missile threats.” THAAD will be added capability to South Korea’s Patriot PAC-2, which it purchased from Germany.

Under a cost-sharing pact, the South Koreans currently pay about 40 percent of the costs of keeping U.S. forces in their country. However, South Korea isn’t paying a nickel of the estimated $1.6 billion cost of the THAAD battery; all it will do is provide the land and build a base. But there is no reason that South Korea can’t pay for its THAAD battery—or batteries, as officials there have previously said they want two—by itself. Indeed, there is no reason South Korea can’t handle its own defense entirely, obviating the need for the 28,500 U.S. troops currently on the Korean peninsula.

Clearly, the immediate military threat to South Korea is North Korea. But South Korea is far richer than North Korea, and thus can afford to maintain a military capable of defending against it. North Korea’s gross domestic product (GDP) is estimated at $40 billion—about on par with the tiny Polynesian island nation of Tuvalu—while South Korea’s economy is more than 30 times larger at $1.3 trillion. According to the CIA, the North “faces chronic economic problems” and its “industrial capital stock is nearly beyond repair as a result of years of underinvestment, shortages of spare parts, and poor maintenance.”

Because North Korea is largely closed off from the rest of the world, estimates vary on how much it spends on its military, but South Korean Defense Minister Han Min-koo believes the number is $10 billion—or about 25 percent of GDP. This is in line with the State Department’s World Military Expenditures and Arms Transfers report estimate. According to the Stockholm International Peace Research Institute, South Korea spends only 2.6 percent of its GDP on defense, but that still amounts to $36 billion—more than three times what North Korea spends.

At a bare minimum, South Korea can afford to pay full freight for the cost of the U.S. forces deployed there. Currently, South Korea is paying about $800 million, but it can clearly afford to pay more. Given that South Korea’s current share is about 40 percent, the total cost should be around $2 billion—though it’s worth noting that the 40 percent estimate may not be accurate. The Congressional Budget Office estimates that an active-duty soldier costs $99,000 a year, which would add up to $2.8 billion, in which case South Korea is currently paying only about 30 percent of the costs.

In addition, the true cost of 28,500 U.S. troops in South Korea is more than the cost of the troops deployed there. Maintaining a professional volunteer military means that the troops deployed overseas must eventually be relieved by fresh troops. If deployments are excessively long or result in being away from home and family too frequently, soldiers may decide that military life is too much of a hardship on them and their families. For an all-volunteer force, the rule of thumb for retaining soldiers over time is a 3:1 rotation ratio (meaning three total units are needed to keep one unit deployed) for active-duty forces. So if it costs $2 billion for the 28,500 troops deployed in South Korea, it really costs much more taking into account the other 57,000 troops needed to be able to rotate deployments.

But even if South Korea is willing to pay for the full cost of U.S. troops, there really is no reason for the U.S. to have 28,500 troops in South Korea. North Korea is not a direct military threat to the United States, so there is no need to put American soldiers at risk. Moreover, if North Korea (with a nearly one-million-man army) decided to invade South Korea, the defense of South Korea would rest primarily with that country’s 700,000-man military, not 28,500 U.S. troops.

Charles V. Peña is a senior fellow with the Defense Priorities Foundation. He has more than 25 years of experience as a policy and program analyst and senior manager, supporting both the Department of Defense and Department of Homeland Security. Peña is the former director of defense-policy studies at the Cato Institute and author of Winning the Un-War: A New Strategy for the War on Terrorism.