SuttaCentral
An3.12
The place where he won victory in battle, establishing himself as foremost in battle. This is the third place. These are the three places an anointed king should commemorate as long as he lives.
Obviously in order to win a victory you must kill and here if I am not mistaken the buddha said a king should venerate the place where the killing event was done
Your thoughts ?
First off, it’s a metaphor. The buddha also called himself a killer, in reference to how he enforced the parajika rules and “killed” monks.
Secondly, you do no not need to kill to win a victory in battle. This is established both within the suttas through the frequent motif of the wheel-turning monarch conquering lands essentially just by showing up with the 7 treasures, and IRL you have examples like the 1859 Pig War or the Ohio-Michigan war.
The Buddha here was reporting a fact, not teaching. It is like you say, an excellent military pilot aim well against the target. That does not mean that you endorse bombing or war. The Blessed One stopped armies and kings to engage in violence more than once.
Sad that the Buddha never imposed his teaching on non-Buddhist, he reminds them that actions caused kamma. The Buddha did not even prevent at the end the extermination of his clan. People, not the Buddha, are responsible for their actions.
The Buddha will not tell you not to become a soldier. He will tell you that being a soldier may put you in a position where you must kill, and if you do, you will suffer the rather horrible karmic consequences. That’s all the Buddha does, and the reason is that part of the non-violence is a non-imposition.
In Religious studies, we call what you are doing here a selective textual reading. Unfortunately, such readings are always misleading since they miss the context and do not consider the overall body of the teaching. 
I think the Buddha is saying that one should bear in mind what is most significant in the gain of arahantship. No matter what greatness has been achieved along the way, going forth, gaining right view and complete destruction of the taints are the foremost. Reminds me of the progression in AN 9.20, where after all the great offerings and deeds described, the Buddha concludes with, “It would be more fruitful develop the perception of impermanence—even for as long as a finger-snap—than to do all of these things, including developing a heart of love for as long as it takes to pull a cow’s udder.”