I've arrived at the opposite conclusion. The root cause of conflict is decentralized power, which is the prediction of realism. Conflict occurs because of security competition, but security competition is only possible when powers are equally matched and trapped in a Prisoner's Dilemma dynamic.
You can sense check this by running through various historic eras. Consider the eras before any nation states, when power was at its most decentralized. That was also when conflict deaths were at their peak due to tribal warfare.
Then move on to the era of kingdoms and then nation-states, and conflict deaths decrease because power centralization increases. Intra-national conflict goes to zero because of a monopoly on violence over that local geography, leaving only inter-national conflict in the structurally anarchic power vacuum.
The peace of the 90s was because the United States was completely dominant and had no reason to do anything because it controlled everything. As the United States declines and power decentralization increases, moves such as denying China access to oil from Venezuela become actions that are deemed necessary in the new security environment. Or a clash between Thailand and Cambodia becomes a thing that can happen, because there is an absence of a big dog to lay down the law, as unjust as that law may be.
The analogy would be a country with multiple privately owned police forces and no single power. You're going to get conflict. It's a structural phenomenon of how power vacuums work when you plop humans inside of them, and it has nothing to do with morality or markets.