Took out the excess words for you. 
ETA: Didn’t see the later posts before, but that’s one good one. Phil did many.
I think of Blowin’ in the Wind as an anti war song, though there’s more to it than that.
And I’d go with “Draft Dodger Rag”. So there.
But seriously, “The Vacant Chair (We Shall Meet but We Shall Miss Him)”, popular on both sides of the US Civil War, is not angry or polemical or bitter, just sad as the bereaved family’s loss sets in.
The voice of caution and reason: Pete Seeger’s “Waist Deep in the Big Muddy” - and the big fool said to push on.
I came to mention this one. Singing “ain’t no time to wonder why, WHOOPIE, we’re all gonna die!” at the top of your lungs is fun and good for firing up the hippies. Too bad it is so specific to a certain time and war.
Many thought Freda Payne’s Band of Gold was a war protest song. I doubt it. But her Bring The Boys Home left no doubt.
Oh wait! I just remembered the last anti-war song to hit the top 40. It’s gotta be Black Eyed Peas Where Is The Love. This came out in the middle of the first Gulf War, I believe.
ANZAC day was last weekend…
And the Band Played Waltzing Matilda
And now every April I sit on my porch
And I watch the parade pass before me
And I watch my old comrades, how proudly they march
Reliving old dreams of past glory
And the old men march slowly, all bent, stiff and sore
The forgotten heroes from a forgotten war
And the young people ask, “What are they marching for?”
And I ask myself the same question
And the band plays Waltzing Matilda
And the old men answer to the call
But year after year their numbers get fewer
Some day no one will march there at all
Waltzing Matilda, Waltzing Matilda
Who’ll go a waltzing Matilda with me
And their ghosts may be heard as you pass the Billabong
Who’ll go a waltzing Matilda with me?
You are correct, sir.
My favorite version:
“The New Recruit” by Michael Blessing (*aka *Mike Nesmith)
Handsome Johnny - Richie Havens
My Mother, the War - 10,000 Maniacs
“Universal Soldier,” Buffy Ste. Marie
Since Ochs has already been mentioned, I’ll toss in "“Where have all the flowers gone?”
Note, BTW, that “The Universal Soldier” and “Handsome Johnny” share a melody (I believe “Universal Soldier” came first)… which is also shared by the chorus of yet another antiwar song, “Snoopy’s Christmas”. 
Courtesy of Clickhole; How Many of These Classic Protest Songs Do You Know?
By three years according to Wikipedia.
Metallica’s One.
Dave Van Ronk, “Luang Prabang”: Luang Prabang (Dave Van Ronk) - YouTube
I really liked Inside Llewyn Davis, but it ignored Van Ronk’s politics.