Chances are its leaders—oligarchs, theocrats, socialists, fascist or communist dictators—for both ideological and economic reasons, set their eyes on militarily weaker, but often freer and more prosperous, neighbors. Eventually, the temptation of a cheap geo-political lunch gets too strong and aggression ensues. This is the leading source of war.
Examples from today’s world include China bringing Hong Kong under its boot (and threatening to do the same with Taiwan), North Korea’s aggression against South Korea checked only by a strong U.S. military presence, Russia’s ambitions to turn Ukraine and other former Soviet republics into vassal states, Iran’s ambitions to spread theocratic statism by supporting terrorism in the Middle East and elsewhere, and Cuba’s infiltration of South and Central American countries.
Think Right or Wrong, Not Left or Right 