Part A Question: What was the importance of the 38th Parallel line in relation to Korean War?(4)

Part B Question: Why did the USA become involved in the resisting the invasion of South Korea? (6)

Typical short answers for Form Three's.Please help me I'm stuck!!!

On 4th august, 1914 britian declared war on germany .The ww1 ended ww2 had begun. less than six years later ensuring peace that followed was labelled 'the peace to end peace ' as if to make this prophetic statement came true , hitlers armies invaded poland twenty years later , on 1st September 1939. two days later, Britain and france upheld their guarantee to poland and declared war on germany for the second time in 25years.japanese aggression in the far east and pacific ww2 into a global conflict by 12 December 1941.when ww2 ended ,it mourned the death of about 70 million victims and witnessed the introduction of the most feared weapon ever invented in the history of mankind - the nuclear bomb.