History. Human nature. The state as leviathan. Sometimes causation is correlated. When nukes came into play, the consequences of violating the peace became to

History. Human nature. The state as leviathan. Sometimes causation is correlated. When nukes came into play, the consequences of violating the peace became too much for any sane state to countenance. The US used nuclear superiority to take on the role of global leviathan. Despite missteps, it used its monopoly on violence as a very big stick that's allowed for a very lengthy peace. If certain idiot regimes keep playing stupid games, we're going to see what happens when the nuclear stick gets used, unfortunately. That might ensure a century or so of peace, if everything doesn't die.