God gave the 6th commandment, then later led the Israelites into the Promised Land and told them to drive out the heathen and leave no one alive.
When Joshua was fighting in the Promised Land God lengthened the day so that they could pursue their enemies longer. Joshua 10:12-14
David was a man after God's own heart, yet his rule was one of war and he was a blessed warrior.
Nehemiah was overseeing the rebuilding of the wall in Jerusalem and made sure everyone was armed and ready to fight if attacked. Nehemiah 4:10-17
Jesus told the Disciples to sell garment to buy a sword. He said two of them was enough. There are not a whole lot of uses for a sword other than fighting/killing. Luke 22:36-38
All this to say that it is pretty clear in the Bible that killing does not equal sin. Hate and murder are sin.