In the Old Testament, God seems to be a warring God, but that is an earthly perspective. God will not impose his authority on humans. He does not want his people on earth using war to accomplish his purposes. He wants his followers on earth to be people of peace.
In the Old Testament age, God had only a few people who walked in the Spirit, because the Holy Spirit could not be released in fullness until after the cross. However, there is a massive battle going on in the spiritual realms. God does not use imposed authority and power to constrain the evil spiritual powers. He uses his authority in the spiritual realms to release his angels to manipulate the struggles between the evil spiritual powers to accomplish his purposes. God does not start wars. He manipulates the outcomes of the wars that have been started by evil spiritual powers.
The powers of evil are not united. They often fight against each other to get better positions in the hierarchy of evil. The Prince of Persia and his followers fought against the Assyrian Spirit and his cohorts.
God mostly accomplished his purposes by sending his angels to fight against the principalities and powers and not letting a different one win. He fought against the spiritual power of Babylon, which allowed the spiritual Prince of Persia to defeat it. This allowed the Persian armies to conquer and destroy Babylon.
God is a god of defence. He works with his people to defend against spiritual and physical attack. However, he is primarily a God of peace, so he always looks for a peaceful outcome. When Moses was leading the people to the promised land, God instructed him to make peace with the people whose land they would pass through (Num 20:17; 21:21-22). If these requests were declined and the Israelites were attacked physically or spiritually, God came to came to their aid in the resulting war.
God sometimes stirs nature to destroy armies, but even then, his first option is peace. This was the case at the Red Sea. God could have destroyed the Egyptian people at any time, if he wanted, but he didn't. He sent Moses to do prophetic signs that would make Pharaoh release the Israelites. Only when Pharaoh's army went after the Israelites intent on killing them did God call on his angels to flood in the Red Sea to destroy his charioteers. The rest of Egyptians carried on living.
During the time when the Israelites were slaves in Egypt, a host of evil spirits flooded the land of Canaan, because they knew God has promised it to Abraham, and they wanted to get there first. God did not want to start a war with the Canaanites, but he had to drive the evil spirits out of the land. The only way to do this was to drive out the Canaanites possessed and controlled by them.
God's plan was to send his angels to stir up natural events that would fill the Canaanites with fear and terror, collapsing city wall and massive hailstones from the sky, dangerous hornets (Joshua 6:20; 10:11; Deut 7:20). The people living in the land would be filled with such fear and terror, that they would flee the land, carrying their evil spirits with them.
I will send my terror ahead of you and throw into confusion every nation you encounter. I will make all your enemies turn their backs and run (Ex 23:27).
This very day I will begin to put the terror and fear of you on all the nations under heaven. They will hear reports of you and will tremble and be in anguish because of you (Deut 2:25).
You saw with your own eyes the great trials, the signs and wonders, the mighty hand and outstretched arm, with which the Lord your God brought you out. The Lord your God will do the same to all the peoples you now fear. Do not be terrified by them, for the Lord your God, who is among you, is a great and awesome God (Deut 7:19-21).
No one will be able to stand against you. The Lord your God, as he promised you, will put the terror and fear of you on the whole land, wherever you go (Deut 11:25).Unfortunately, Joshua did not understand God's plan and started a war against the Canaanite kings. This tight contact allowed the evil spirits to stay in land by jumping across to the victorious invading armies (see Violence and the Old Testament).
Spiritual WarUnderstanding the determination of the spiritual powers of evil explains much of the violence in the Old Testament.
Whenever God gained authority to act on earth, they reacted with dreadful violence on earth. This often left God with no option, but to use violence against them.
Prior to the cross, the only way to deal with evil spirits was to separate from the people and things carrying them.
Principalities and powers used military empires to control the world. The only way that God could constrain them was to stir up other military power against them.
Although God has proved his reliability again and again, the children of Israel seldom had sufficient faith to trust in him for their defence. They constantly rejected his way, and chose to defend themselves with military power. He often had to intervene in wars that they had started to protect his people and position.