As with Mexico and virtually any other nation that isn't the United States -- or part of it, with the exception of Puerto Rico and Hawaii -- President Trump went after South Korea, saying that they were going to pay for the THAAD missile system which was agreed to be sent to them last July. The Missile Defense System was being negotiated on by both the U.S. and South Korea in order to protect them from incoming missiles being fired by North Korea, should they ever try, similar to the deal the U.S. has with Israel and their Iron Dome missile defense system.
U.S. defense funding and Trump
In comparison, it's known that the U.S. already gives Israel billions of dollars each year for their defense, and under President Obama, the Iron Dome defense system was funded by the U.S. Congress in 2011-2012 and again in 2014. While Trump has said that South Korea would pay for it, Trump's national security advisor HR McMaster corrected the statement, saying that the U.S. would shoulder the cost. On May 2, the U.S. military said that the system was now operational.
One would think that for a President who single-handedly picked a fight with North Korea, and even considered going it alone without the only nation in the area that has any leverage, China; would just go ahead and give the system to South Korea, since they would be the first nation to be targeted in a conflict that Trump is instigating from afar.
A South Korean paper (Chosn Ilbo) said that the fact that Trump is making this a matter of money and the economy was undermining basic trust with South Korea.
Controversial THAAD system
The system itself is already very controversial for the area, with many South Koreans protesting THAAD, saying that it would bring instability to the region.
China has also expressed anxiety, as well as Russia, for the same reasons. Both countries have promised to install their own systems as well. However, South Korea was already attacked with artillery fire and missiles from the North back in 2010 where cannons that were set up to defend them, didn't. The island that was attacked was Yeonpyeong, where it's said that a military base was hit, along with homes, a town hall and more.
The North Korean military fired on them during a military training exercise like many that are taking place now. The South Korean Military responded, hitting their barracks, command structures, and multiple rocket launchers. The North claimed that shells from the training exercise were landing in their waters which the South Korean military denies, saying they were landing in the opposite direction. Residents in the area said that they felt a lot safer with the presence of U.S. forces there when they arrived.
