Tao Teh Ching Chapter 31

夫兵者，不祥之器，物或恶之，故有道者不处。
君子居则贵左，用兵则贵右。兵者不祥之器，非君子之器，不得已而用之，恬淡为上。胜而不美，而美之者，是乐杀人。夫乐杀人者，则不可得志于天下矣。
吉事尚左，凶事尚右。偏将军居左，上将军居右，言以丧礼处之。杀人之众，以悲哀泣之，战胜以丧礼处之。

Translation
A weapon is an instrument of evil omen, it is disliked by all creatures, thus is the reason the man with the Tao will not get close to it.
The gentlemen prefer to reside on the left when in their own house but honor the right when involved in military action. As an instrument of evil omen, the weapons therefore are not instruments for the gentlemen. It is only used when circumstances are such that a gentleman has to use it in spite of himself, and even in using it, he choses a very controlled fashion. A gentleman will not glorify his victory. Those who glorify their victories take pleasure in killing and these people cannot rule the world.
In events of joyful nature, the left side is esteemed; in events of disastrous nature, the right side is honoured. The second commander resides the left and the general resides to the right. This arrangement is the same as that of a funeral. When mass killing happens (as a result of war), deep mourning is set for the killed and the winning side holds the funeral for the dead.

Comments
This chapter expends Lao Tzu’s view of war. He did not say that you should avoid war all together. This is bit different from a Buddhist’s view. The essence here is 不得已而用之，恬淡为上. That is it is carried out only when absolutely necessary and when he does, he carry it out without obsession. The gentleman kills, but only as a last resort and he take no pleasure from his killing. In fact, he mourns the victims of war.
I hope and pray that such necessity do not arise often. It is already blessed that the world is in general peace for quite some time. Let us pray that we harm less living beings during our own lifetime.