The US actively supported South Korea and led to its formation during the three-year-period from 1945-1948 when the regime was crystallizing. It also galvanized UN support and supplied most of the troops to help South Korea defend itself against North Korean aggression and attempted conquest. To this day, thousands of US soldiers patrol the border between the two Koreas to protect South Korea from any future military conflict. South Korea also has also relied on the US for economic support, the most recent evidence of which is the US-ROK Free Trade Agreement.
It was called a "police action"
South Korea welcomed us, North Korea fought us.
The truman doctrine
Yes North Korea does not like the US mainly because of the country's involvement in the Korean War between North and South Korea.
North Korea's becoming nuclear power and extending continuous threat to South Korea which is an ally of USA, led the later to intervene and get involved.
money
Korea's history is closed tied to China. China is Korea's closest neighbor.
Korea, like any other countries, faced countless wars throughout history. Korea has a history of 5000 years and no country's history is without wars.
South Korea remained free of communist control.
Korea gave tribute to mainland China
The invasion of the Republic of Korea by the Democratic People's Republic of Korea (Noth by South).
South Korea remained free of communist control.