This is an interesting phrasing when juxtaposed with the title, and one that I think deserves attention, especially on HN. Being "anti-war" is about the worst rhetorical position one can take - nor does it actually reflect the truths of what a sensible person believes about "war".
There are bad people in the world, some of those become powerful people and inflict their badness widely. Sometimes you can reason and guide these people but not usually. That's where diplomacy comes in, diplomacy can deter activity away from the source of conflict. Sometimes diplomacy is ignored repeatedly, or worked around. Tensions escalate, stalemates are reached, and the diplomacy tool bag is left empty. War is the last tool available to modern government in order to preserve it's way of life. Categorically, war is a tool to be respected - much like a powerful drug. Its why warrior cultures and ethos grew out of the activity and remain in-tact today around the world.
Picasso's piece, to me, was not anti-war - anti-war would mean, in this context, let the person willing to inflict the most violence against me have their way. It's anti-tyrrany, which is what was happening at the time. Words mean things, and I think people that explain things the way this piece starts out do so intentionally, and that is regrettable.