Well, there's another fun topic. Here are my two cents worth.
The peaceful, non-intrusive coexistence of nations requires a high level of intellectual and spiritual evolution that we may never reach. After millennia of international intrigues, expansionism, colonialism, conquests, invasions, and overt and covert foreign interventions across the globe, we humans are still stupid and greedy enough not to have learned our lesson, despite the inevitable destruction and suffering.
As for the United States in particular, which were mostly founded on the genocide of the indigenous Indians, let's just name a few countries were we intervened, many a time overthrowing democratically elected governments, and count the corpses: Vietnam, Irak, Korea, Chile, El Salvador, Cuba, Philippines, Afghanistan, Honduras, Libya, Grenada, Iran, etc etc etc.