Peace historian Kent Shifferd (2011) describes this in four major areas: "international institutions, international law, the sovereign state, and local government" (p. 173).
International institutions in our modern era are indeed a modern invention, though some institutions historically have played that role informally--e.g. the Catholic Church, as it both proselytized and issued papal decisions. Similar efforts by other religions--however successful in the aggregate of conversion, have not combined the success of one sect and the formalized central rule of that sect enough to have the same institutionalized effect that intersected in Catholicism. Most international institutions, however, are modern and most are secular. All--whether governmental or nongovernmental--have an effect on the norms and practices of either violence or nonviolence. All are open to change. The UN already tends toward nonviolence and can be further developed, especially by reforming the Security Council. The worst are military alliances and the worst of those is NATO, once a nearly unused defensive and deterrent alliance and now in the post-Cold War world a swaggering bully arrogant to make violent practice its norm--e.g. Afghanistan, and Libya. Increasing the hold of the nonviolent tendencies in the UN and diminishing the power and reach of NATO are important goals on the nonviolent agenda. These are both possibilities.
International law is relatively new and is evolving toward nonviolence in several ways, and needs prodding and attention in order to continue and accelerate that process. Finally, thanks to Jody Williams and her NGO coalition of global grassroots groups operating in partnership with a select and then increasing number of sovereign states, powerful international law was created by the people power on our planet. This can continue. We could outlaw war profiteering and remove the real driver behind the nominal reasons for war, for example. We could outlaw arms transfers altogether. We the people of Earth have that power if we self-organize toward nonviolence. It has been done from below and that is not easy nor fast, unless we compare it to waiting for the elites to make meaningful moves.
I teach in a program with many international students and many Americans who want to go work internationally to help make peace. This is great. I tend to focus on the students who want to fix America first and I do this for several reasons. One, this is my country, I love it dearly (the country, not the government), and I see that love in some of my students. Two, a citizen of a country has more impact at home than in someone else's country, both legally and culturally, usually. Three, my country has the biggest military budget on Earth, the most military bases on other people's soil, exports the most weaponry to fuel other violence around the world and to prop up dictators, and my country has led the world in invasions of other nations in the past few decades. Finally, Americans live in a democracy and everything done by our government is not only paid for by us but is done in our names. So, I try to have some effect on our sovereign nation-state and encourage others wherever they live to make attempts in their homelands too. All the theories and case studies of nonviolence show that this is the most effective process.
Local governments are the most accessible and directly affect us no matter where we live. Yes, we don't immediately change the world when we change our local governments, but the impacts are obvious to those who are affected right in front of us. From retraining police to promoting neighborhood mediation and much more, our local governments are institutions that we can change.
Creating our own institutions is also done daily in our society and the US is historically a fertile field for this. Some of those institutions have promoted nonviolence powerfully and those need strengthening. Others need to be created. This is important life work, paid and unpaid, part-time or full-time, and always worthy. Literally, there is no work more urgent nor crucial. We can not only work for these civil society institutions, we can support them with the fruits of our labor, both monetarily and in-kind. Find your favorites and give and give. You are doing the work of the generations. Thinking seven generations from now, no one will know my name and it's possible no one will know yours, but together we can give them a chance for a life if we make good decisions right now.
Shifferd, Kent D. (2011). From war to peace: A guide to the next hundred years. Jefferson, NC: McFarland.