Intervening in other countries conflicts is a controversial practice and not one that is guaranteed to work. The US should be very selective of what conflicts they get involved in. Some interventions have been pointless, overthrowing the Nicaragua government, the trade blockade on Cuba and the Vietnam war were all uncalled for. However some interventions can better the countries and the world as a whole. The US backclash of Iraq is the main reason they have been so timid and tame in confronting ISIS. And because of this ISIS have been able to grow extraordinarily and are now an extremely powerful organization that has caused serious harm. If the US had intervened straight away the problem would have been solved already.
The same is true of North Korea. The North Korean people suffer inhumane human rights violations, and they lack the capacity adn ability to do anything about it. Countires that have the ability to do something about it, should step up and help when they can.
The United States ought to aid, where possible, in just wars, especially if its allies are involved. Should some foreign power unjustly invade another, or commit various atrocities, and the United States were to be in a position to help, it would be unjust to allow the evils to continue based on the principle that it is not yet directly involved.
The US has been acting as a security force for the world for too long. Although it was appropriate to go into Afghanistan after 911, we should have stayed out of Iraq. Invading Iraq has lead to the rise of ISIS and other radical Islamic groups vying for power in the Middle East.
With more than 5-percent of the U.S. population unemployed and at least 15-percent living in poverty, the U.S. needs to take care of its own citizens first, before sticking its nose into the affairs of other countries. Soldiers sent to fight in these conflicts come home suffering from lifelong injuries and mental illness that America tends to overlook and the government continues sending these people into battles that have nothing to do with them.
There are times when it may seem necessary to intervene other wise the United States could end up paying the ultimate price themselves, for example 9/11. But there are times we need to stay out of it such as with Vietnam or Iraq. In both cases the United States had no business sticking their nose in the matter. Iraq really wasn't our business to get in the middle of, we had no choice but to go to Afghanistan but Iraq there were no weapons there, so we had no business being there.