There is ample historical evidence that having an army to send into war makes the world less safe, not more.
If the US army in particular had a clear conscience, why would the US oppose the International Criminal Court in The Hague? Telling your soldies that their war crimes will go unpunished is a great way to invite them.
I was against the war in Iraq and still am, but IMO the jury is still out whether the war in Iraq made the world less safe. Saddam was a brutal dictator including gassing and genociding the Kurds. The Kurds now have a fairly stable government in Northern Iraq thanks to the invasion and are a center of prosperity in the region. ISIS has been largely suppressed, and there's been no repeat of the Iran or Kuwait wars of Iraq since the US takoever.
The aftermath of the Iraq invasion led to the deaths of hundreds of thousands of civilians. It doesn't seem unlikely that Saddam would have killed fewer than that.
If the US army in particular had a clear conscience, why would the US oppose the International Criminal Court in The Hague? Telling your soldies that their war crimes will go unpunished is a great way to invite them.