That would be the samuri.
no
No South Korea did not invade North. North and South used to be a whole and was together until the North wanted a communist Dictatorship. People denied because they wanted freedom of speech. They had war so then South and North are now split.
Japan
except city called Busan everything was invaded
North Korea invaded South Korea. Exactly, the Korean war started by North Korean army's attack to the 38th parallel (a line of latitude used to divide the Korean Peninsula) at about 4AM on June 25, 1950. However, North Korean propaganda claims that South Korea attacked first. (No country outside of North Korea agrees with this view.)
Japan invaded Korea first, then China during WW II, if that is what you are asking.
June 25, 1950 was the first date of the Korean War, and saw South Korea invaded by North Korea.
To restore South Korea after it had been invaded by North Korea. The US invaded Korea twice. The first time was in 1945 when the US and the USSR agreed to invade the Korean Peninsula to defeat the ruling Japanese. The USSR invaded from the north and, as agreed, stopped at the 38th parallel. The US invaded from the south and stopped at the same line. The second time, in 1950, the US only invaded North Korea. The Republic of Korea (South Korea) requested US assistance, so when the US entered South Korea it was by invitation, not invasion. The invasion of North Korea was part of the objective of eliminating the North Korean ability to effectively re-invade South Korea.
Korea
being the first deliberate expansionist
Canada.
The Korean War was the FIRST "Hot" battle of the COLD WAR. The Cold War was a non-shooting (no violence) stand-off between the communist world and the free world. Communist North Korea invaded South Korea; a clear case of self defense.
North Korea. The war started when North Korea invaded South Korea in an attempt to unify the Korean peninsula for communism. (Later in the war, China became involved, so the UN force was also engaged with the Chinese army.)
Member countries of the UN supplied troops and war materials to aid South Korea.