I have looked a bit in the bible for this answer, and perhaps I am dumb, but where in Christian tenets is the belief that Christianity ever should have political power?

I mean, I saw that Jesus would come back again and be the king of the world, and I get the JW's at my door telling me that their church is the kingdom being prepared for God, but where is the actual teaching that the church should be in charge or have authority? Why did the early Christians want authority?

In my mind a church is something distinct and separate from government. Government is made from people unifying together with similar cultures/lifestyles.