I didn’t say it had to be a good reason, or a valid one. I said a reason.
Most citizens of the USA (I would like to think) wouldn’t support a war just for the sake of going to war.
Enemy - Definition and More from the Free Merriam-Webster Dictionary
In this case, I would define an enemy as an entity that presents an unacceptable threat to that which you must protect, which in the case of the US government is the USA itself.1 : one that is antagonistic to another; especially : one seeking to injure, overthrow, or confound an opponent
2 : something harmful or deadly <alcohol was his greatest enemy>
3 a : a military adversary b : a hostile unit or force
Of course, then you would have to define an “unacceptable threat” and “must protect”.
That is up to the officials who are elected to do so. And their views probably differ at least slightly from my own, for various reasons.
As an example of a preemptive action situation, suppose you were in charge of the military defense of the USA, and you had received strong intelligence that Mexico was planning to launch a full-scale invasion of Texas.
Assume that Mexico had a comparable military strength available in that area.
Obviously, diplomatic actions would be attempted to stop this.
But if diplomatic means failed, or intelligence that Mexico was moving ahead with invasion plans, and using the diplomatic discussions as a cover, came into your possession, what would you do?
Wait too long, believing that Mexico would back down, and you might have enemy troops in Texas.
Move too soon, believing that Mexico would not back down, and you would have attacked a neighbor of the USA.
Now, obviously, this situation is highly unlikely, and would depend on many not currently in place situations and conditions to actually come to pass…But you get the idea…
The problem with intelligence is, you can only extremely rarely be 100%, or even 90% sure about something.
Thus, you would receive less income from the exportation of said good because of the other countries production of said good at a lower cost.
Not enough of one to warrant an invasion/attack on the other country in my book, but my book isn't necessarily the book in use.
This was a somewhat simplified example, but you get the idea.
Suppose a country’s system of government was a dictatorship. Said dictatorship could control the press and many other aspects of information transfer to their population, but not 100%, and ideas/info from outside the dictatorship leaked into the population, causing them to become restless, due to observation of better conditions of freedom/whatever in another state with a different government system.
If dictatorship is sufficiently powerful, options include military subjugation of state with government system casting negative light on dictatorship.
I said: “…If an opponent poses no threat whatsoever, I wouldn’t see the point in attacking them. Unless you are trying to build an empire, and just want their stuff. But that’s another discussion entirely.”