"The USA were in Viet Nam to prevent a massive communist block from overtaking SE Asia."

Soooo, the phosphate mines had no bearing on the military incursion (it was NEVER a "war")? Did the west not want the phosphate VERY badly?... so much so that they were willing to wage "war" to get it? ... under false pretenses?

Ideologies? Resources?

I pick resources. Ideologies are merely excuses for the extraction of resources by force.