I think of myself as antiwar, but I have to agree that this assignment sounds politically motivated. It would be far more appropriate to have students choose a war-era song and not specify that it has to be antiwar. Just my 2 cents.
A few antiwar songs...
Knocking on Heaven's Door, Bob Dylan
Fortunate Son--Creedence Clearwater Revival (really more of a protest of a particular policy of the war)
Traveling Soldier--Dixie Chicks (from the 'war is sad, soldiers die' school of protest).
For you to be here now, trillions of drifting atoms had somehow to assemble in an intricate and intriguingly obliging manner to create you. It's an arrangement so specialized and particular that it has never been tried before and will only exist this once.
--Bill Bryson, "A Short History of Nearly Everything"