Short term: Bring whoever is responsible for the New York/Washington atrocities in front of an international court, as far as they are still alive. Do so with calm. Do not follow a logic of escalation. Avoid civil casualties, and talk about it, and try to prove that you did so. Benevolent people all over the world are watching for signs of sincerity like this.

Middle term: The US have to pay their 2 billion debts to the UN. The UN are a crucial institution for resolving conflicts, and the US should show respect to them instead of hindering their work, otherwise noone on this planet will feel obliged to show respect or support the UN.

Long term: Listen to each other. Talk until you understand what's at stake. If you don't understand, you didn't talk long enough. And if you do understand, behave accordingly, and don't pretend you didn't. Human beings have the capacity to see the world from someone else's standpoint. Use this capacity. Any other kind of peace, I'm afraid, can only be sustained through the continuous exertion of military force and will finally lead to an Orwellian world where nobody can feel safe lest pursue happiness.