In the 1950's, Korea was divided into North Korea which installed a communist government by the Soviet Union an South Korea which installed a capitalist government from the United States
I protect the capitalist side!
And I protect the communist side!
Later, North Korea wanted to invade South Korea and unite the country as communist and South Koreans didn't want to become communists. This then led to war.
We will unite the country as communists!!!!
After North Korea refused to withdraw its troops as an order from the United Nations and continued to invade, U.S. president Harry Truman decided to send forces to South Korea to help them in the war from becoming communists.
Send forces to South Korea and help its people. We can't let them become communists!
And so the war continued.
After the war that lasted 3 years, the U.S. had helped South Korea get a victory with a lot of deaths however so there was a cost.
Ever since the Korean War the U.S. promised to help protect the border line of Korea to help protect South Korea from any possible future invasions. Yes North Korea still communist and South Korea is still capitalist.
From now on, we will help you in case of any future invasions.