Well in this case it was the fact that whoever won between these two was going to be a problem after nearly certainly (as shown by Russia in fact doing so). So the smarter option was to weaken one while removing the other.

Its pragmatic because its certain more wars were to follow, so it benefits the ordinary American by not sending their sons to another war a decade later and then a decade after that too, which is what ended up happening.

If Europe could handle itself rather than let Germany, twice, and then Russia cause global reaching problems, then I'd say that its not our business and to stay isolationist. But history has shown they literally cannot stop warring, and in an increasingly globalized world that is all of our problem.