First, the peace Jesus gives is not the peace that this world gives. Maybe we should understand what His definition of peace is. I found this excerpt from Baker’s Evangelical Dictionary of Biblical Theology:
The Meaning of Peace. In English, the word “peace” conjures up a passive picture, one showing an absence of civil disturbance or hostilities, or a personality free from internal and external strife. The biblical concept of peace is larger than that and rests heavily on the Hebrew root slm, which means “to be complete” or “to be sound.” The verb conveys both a dynamic and a static meaning—”to be complete or whole” or “to live well.” The noun had many nuances, but can be grouped into four categories: (1) salom – as wholeness of life or body (i.e., health); (2) salom – as right relationship or harmony between two parties or people, often established by a covenant (see “covenant of peace” in Num 25:12-13; Isa 54:10; Ezek 34:25-26) and, when related to Yahweh, the covenant was renewed or maintained with a “peace offering”; (3) salom – as prosperity, success, or fulfillment (see Lev 26:3-9); and (4) salom – as victory over one’s enemies or absence of war. Salom was used in both greetings and farewells. It was meant to act as a blessing on the one to whom it was spoken: “May your life be filled with health, prosperity, and victory.” As an adjective, it expressed completeness and safety. In the New Testament, the Greek word eirene is the word most often translated by the word “peace.” Although there is some overlap in their meanings, the Hebrew word salom is broader in its usage, and, in fact, has greatly influenced the New Testament’s use of eirene.
Secondly, to all those who say God would never condone war, I ask you this:
What is to be said about this scripture found in the New Testament (inspired by God, I might add)?
Therefore whoever resists authority resists what God has appointed, and those who resist will incur judgment. For rulers are not a terror to good conduct, but to bad. Do you wish to have no fear of the authority? Then do what is good, and you will receive its approval; for it is God’s servant for your good. But if you do what is wrong, you should be afraid, for the authority does not bear the sword in vain! It is the servant of God to execute wrath on the wrongdoer.