Question:
In the Ten Commandments it says, "Thou shalt not kill." Can you explain to me why that Scripture is in the Bible when God told the children of Israel to fight so many times and to destroy their enemies?

Answer:
Old Testament
The word translated kills in the Old Testament was ratsach, meaning literally "to murder" - Exodus 20:13

Any death in keeping with God's Word and sanctioned by the government is not defined as murder - Exodus 21:12, Genesis 9:6

Old Testament rules of war
Excused from military duty
In hardship cases - Deuteronomy 20:5-7
Because of fear - Deuteronomy 20:8
Women and children spared - Deuteronomy 20:14
Enemy given opportunity to surrender - 1 Samuel 11:2-3; 30:1-2
Total destruction ordered for corrupting influences - Deuteronomy 20:26-18

New Testament soldiers
Held positions of honor - Acts 10:1-5, 34-35; 2 Timothy 2:4
A model for Christians - Ephesians 6:11-17