We are taught in Romans 12:18 (KJV), "If it be possible, as much as lieth in you, live peaceably with all men."
"IF IT BE POSSIBLE!!!"
When Paul wrote this, it was with the understanding the SOME persons are so bad that we just can NOT live peaceably with them. We are to love our enemies, but sometimes they need an 'attitude adjustment' so you can get their attention.
That is one reason why wars are waged.