The principles of civil government are primarily set out in the Old Testament. We want a king over us. Then we will be like all the other nations, with a king to lead us and to go out before us and fight our battles (1 Sam 8:19,20).
Only two two civil authority roles can be justified from the Old Testament: the military leader and the judges.
I do not include kings, because the king was a sub-optimal option. A king was really just a permanent military leader.
Israel did not need a permanent military leader, because God had promised to protect them. Moses and Joshua took the military leader role until Israel had conquered the promised land. No successor to Joshua was appointed, because the role became unnecessary once they had conquerred the land. God has promised to protect them and keep them safe from invasion.
Israel only needed a military leader when they lost God’s protection by turning away from him. According to the book of Judges, this happened quite frequently. The people would become complacent and stop trusting in God. He would withdraw their protection and they would be invaded. When the nation repented, God would send them a military leader to rescue them from their invaders.
Israel wanted a king because they had become dissatisfied with just having judges. Judges were fine as long as the nation obeyed and honoured God, and he protected them from attack. However, they lost his protection so frequently, they wanted permanent military protection. So they asked for a king like the nations around them.
The king was not a new role, but a permanent form of a temporary one. Israel wanted a king, so they could live in permanent disobedience to God without threat of invasion.
The full series can be found in Government of God and Judges
We want a king over us. Then we will be like all the other nations, with a king to lead us and to go out before us and fight our battles (1 Sam 8:19,20).