Firstly, who said war with Greenland? They want to buy Greenland, This is not new and the US has proposed this many times and has considered it many more: https

Firstly, who said war with Greenland? They want to buy Greenland, This is not new and the US has proposed this many times and has considered it many more: https://en.wikipedia.org/wiki/Proposed_United_States_acquisition_of_Greenland https://en.wikipedia.org/wiki/Proposed_United_States_acquisi... Leaving that aside, the US is hugely more powerful than Denmark, Panama and Canada combined. If could walk over all three right now - no need for increased military expenditure. Iran has been preparing to fight the US, and will probably have fanatics who will fight on after defeat of the military creating an Iraq like situation - but AFAIK the direction of expenditure is wrong for that as preparing for that would require spending on counter insurgency and boots on the ground. There would also be lots of support from other countries in the region for that. The ONLY country that is a peer rival to the US is China. Other nuclear powers are probably able to deter the US, but only China can actually fight it in a conventional war.