Note that there is a difference between the ape-men battles and the later wars men fought amongst eachother.

By influencing the mind of Moon-Watcher in our distant past, the monolith effectively created a separate breed of man-apes. The forebearers of our race became smarter than other tribes of man-apes. Figthing the 'lesser men' can therefore be seen as competing with another, distinct and separate species for 'lebensraum'; in fact, the tribe discovers they can kill prey for food. All killing is directly related to survival.

In our modern age, things are different. The fighting now is between equals, and the reason is not survival, but it is (mostly) politically motivated.

That might not be a scenario the Monoliths were counting on; the fighting done in the two time-frames can be judged on an entirely different premise and a different conclusion can be reached.

Note that there is a difference between the ape-men battles and the later wars men fought among each other.

By influencing the mind of Moon-Watcher in our distant past, the monolith effectively created a separate breed of man-apes. The fore-bearers of our race became smarter than other tribes of man-apes. Fighting the 'lesser men' can therefore be seen as competing with another, distinct and separate species for 'lebensraum'; in fact, the tribe discovers they can kill prey for food. All killing - for food or for protection and 'space' - is directly related to survival.

In our modern age, things are different. The fighting now is between equals, and the reason is not survival, but it is (mostly) politically motivated. It no longer serves the survival of the species, but - while one group might gain an advantage over another - the species as a whole deteriorates in war.

The latter might not be a scenario the Monoliths were counting on; the fighting done in the two time-frames can be judged on an entirely different premise and a different conclusion can be reached.