Can somebody please answer this question for me cause id tried my best researching but I need more answers..
'why did USA join the first world war?'

Here's an article you'll find helpful:
http://www.socialstudieshelp.com/Lesson_72_Notes.htm

The Americans were neutral in the war.

They delivered supplies to Great Britain.

Germany shot down one of its ships (or a sub) since they were “helping” the enemy.

The Americans did not like it.

They joined forced with Great Britain, Canada, etc. and took on Germany et all.

At least, that is what I remember from my history class back in high school.