Let's look at the beginning and the end of the Korean War (for
both sides) and then compare:
1)Beginning
USA first entered the war with the purpose of toppling North Korea.
To destroy the North Korean communist. For this purpose, USA lead
the whole UN army incursion into North Korea.
China entered the war LATER, after USA troops had already overrun
almost the whole of North Korea up until the border with China. The
goal of China's army was to drive the USA out of North Korea. To
visualise this, you must know that Korea is a peninsula. The
peninsula was divided into North Korea and South Korea. To the
north of North Korea, it's adjoining with China. I know some of you
don't have much knowledge of the geography, but you can imagine
Korea as the Malaysian Peninsula, and China's location as Thailand.
Then North Korea would be like from KL onwards until the border
with Thailand. Can visualise?
2)End
The war ended with a cease-fire at the 38th parallel, which was
almost at the original border between North Korea and South Korea.
In other words, after China entered the war, the whole USA led UN
army was driven completely out of North Korea. At some point, USA
army retreated almost to the southern part of South Korea (like JB
in Malaysia). Then the cease-fire agreement was reached, with the
border set at 38th parallel.
3)Comparison
So now, do you think USA succeeded or failed in the Korean War? And
don't talk to me about casualties. The definition of success and
failure is whether the goal of the war was achieved or
not.