A country that is either becoming too powerful or has the potential to, and/or has the key to sway the regional power dynamics, key resources, or is causing trouble to an ally, or are arming themselves, historic animosity, land grabbing intent, perceived threat ... more criteria can be added to this list.
Such a country's progress should be thwarted, so that their own positions are safe.
This has been the case always in history, Kingdoms or Nations, whatever the entity is called. Of course, spreading a religion was another cause, like in the case of the Crusades.
That's all it boils down to.
The rhetoric of protecting Human rights, removal of dictatorial regimes, all that is just fluff to disguise the true intent.
But, even if there was such a genuine intent, imposing western democracy isn't necessarily the required/best option.
The country in question quite often has complex dynamics and is far more heterogeneous than a typical western democracy. It's a different system of governance that it needs. It's a very colonial/supremacist mindset to think that somehow western countries know better how to govern the country in question.
Human rights violations are better addressed by a world body than individual countries. And there should be a blanket ban on military intervention by any country.
In some ways, Trump atleast has made his intent clear, that it's the oil/natural resources that he is interested in, Venezuela, Iran, Greenland, -- unlike other world leaders (think Tony Blair justifying this war, albeit articulated in a much more polished way, devoid of obsceneties) who would try and make a show of how they are trying to spread western democratic values and to help the people of that country (that they are bombing!).
That the might of the American Military has been showcased to the world now, it's going to make every country to increase their defence spending. NATO countries have already been forced to do so. Apparently, European countries have been spending too much on their social welfare schemes!
And if you want to be cynical, US leads the world in arms manufacture. So, there's that.
Probably nuclear proliferation will increase too. As was observed by a PP, the countries which aren't nuclear powers/part of an alliance like NATO, have found themselves really exposed. US wouldn't dare to "intervene"in North Korea for example, though they have bases in South Korea.