What reason did USA have to join the Vietnam War?

if it was that incident where a navy ship was sunk which doesnt even present any phisical proof who knows it could just be the governemnt saying that just to get into the war and why was the ship there in the first place? and even if it was sunk was it really neccary to stay in vietnam for 10 years and kill thousands of inocent people and end up loosing the war anyway? personally i think that america is a bully to other countries and looks for the smallest reason to start an all out war like cant they resolve issues in a more peacefull way i mean if it was somehting as big as 9/11 then sure they have a reason to join the war but ONE navy ship with no physicall proof i mean come on atleast give some pictures or videos or somehting the same thing is happening in iraq wheres the so called "weapons of m destruction" and what did iraq have to do with 9/11 they killed saddam hussein why nto get out of there now instead of stealing their oil