Interesting and unnerving analysis of what could happen if Piggy invaded Greenland:

[ancianita]

40. But the US military has.

You say they might not do this, but so far no order to invade an ally under NATO has been given, and so this will be the US military's point of refusal. I think you can feel confident about that.

Were the U.S. Military to break the law and follow the felon's order to attack a NATO ally, then the USA commits an act of war, at which point all foreign treaties are rendered null and void, and the USA becomes a rogue state sponsor of terrorism internationally.
The U.N. can eject the USA from its security council. Other serious international trade consequences will follow.