Many people misquote the ten commandments and say that killings is wrong when it actually says murder is wrong. Also, the ten commandments refer to human relationships and not government. Based on that understanding, is war ever justified? Is it justified to defeat evil? Does a government have that right? Examples: The American invasion of Afghanistan to defeat terrorism, World War II.
Though war is a terrible thing, and innocent lives are lost, sometimes war is required to restrain evil. Sometimes the only way to keep sinful people from doing great harm is by going to war with them. If Hitler had not been defeated in World War II, how many more millions of Jews would have been killed? If the Civil War had not been fought, how much longer would African Americans have had to suffer as slaves? Therefore for the Christian, going to war would be a valid option, and a part of submitting to the ruling authorities as required in Romans 13.
However, the most important thing we can be doing in a time of war is to be praying for godly wisdom for our leaders, praying for the safety of our military, praying for quick resolution to the conflict, and praying for minimum casualties – on both sides of the conflict.
Also read this article concerning your very question.
[Answered by Pastor Quang and Pastor HM]