Songs/music on the theme of peace/anti-war

I am once again setting the local pub quiz and we will do it in aid of Parkinsons UK, as my OH has PD.

I usually have a music round, which consists of playing music and asking people to identify something - title, performer, composer etc. This time I would like the round to be a tribute to Pete Seeger who has recently died, so I thought a peace/anti-war theme would be good.

I am interested in any suggestions that people might have for this. I have all the usual suspects, but would be glad to hear your ideas, particularly classical pieces/songs that have this as their theme.

Lots of thanks for your help.