It is the 80th anniversary of D-Day. I just finished watching the ceremony in France, where they honored WWII vets who still live, and those who never came home. It was incredibly moving.  But we can't just look back and grow emotional during inspiring video montages. We must think about how to avoid the paths of division that could send future young men and women to similar fates. We can honor those brave WWII vets further — now — by listening to those who are trying to help us remember how to resolve our differences peacefully, rather than through violence or force. Yuval Levin is one of those people. My interview with him about his new book, out next week, "American Covenant: How the Constitution Unified Our Nation -- And Could Again." Yuval's argument is that our Constitution is more than a legal document, though it is that. The Constitution is also a blueprint, a map, which lays out how our nation was intended to solve problems and resolve disagreements. James Madison, the nation's fourth president, was one of the chief architects of our constitutional system. And our system has a psychology of sorts, Yuval's book says. This system defines unity as acting together even when we don’t agree. Madison and others designed an architecture of checks and balances and disparate power centers that are intended to pull and push us into engagement with those who are different and think different. It is that action together which creates common purpose and cohesion, a unity of "peace but not quiet," as Yuval writes. "Politics is haggling, or it is force," he quotes Daniel Bell as saying. He adds: "We have forgotten that the only real alternative to a politics of bargaining and accommodation in a vast and diverse society is a politics of violent hostility." Many Americans despair that we can repair our divisions. But Levin rejects that despair. He calls his book "hopeful" but says that does not mean he is necessarily optimistic. "Optimism and pessimism are both dangerous vices, because they are both invitations to passivity," he writes. "Hope is a virtue, and so it sits between those vices. It tells us that things could go well and invites us to take action that might help make that happen and might make us worth of it happening." The way we move toward this unity of "peace but not quiet" is by thinking more carefully about how our system is structured, and what kind of behavior it incentivizes: cooperation across difference as the Constitution intended, or pulling apart, demonizing the other side and fearing those who disagree, and performative outrage.