The lyrics of "Fortunate Son" pertain to multiple wars that America has been involved in, not just Vietnam.
Let's break it down:
"Some folks are born made to wave the flag" - all
Ooh, they're red, white and blue - all
"And when the band plays 'Hail to the chief'" - since the Civil War
"Ooh, they'll point the cannon at you, Lord" - all, mainly up to the Civil War
"It ain't me, it ain't me/I ain't no senator's/millionaire's/military son, son/It ain't me, it ain't me/I ain't no fortunate one, no"
"Some folks are born silver spoon in hand" - all
"Lord, don't they help themselves, oh" - all
"But when the taxman comes to the door" - all, particularly the American Revolution
"Lord, the house looks like a rummage sale, yes" - all
"Some folks inherit star spangled eyes" - all since the War of 1812
"Ooh, they send you down to war, Lord" - all
"And when you ask them, 'How much should we give?'" - all
"Ooh, they'll only answer 'More! more! more!'" - all\\
