"And Jesus came and spoke to them, saying, 'All authority has been given to Me in heaven and on earth. Go therefore and make disciples of all the nations, baptizing them . . . ' "
Precisely *because* the Lord Jesus Christ possesses *all* the authority of the church *and* the state, (in heaven and on earth)--His ministers and parishioners may go into all the world, baptizing and making disciples. Notice that no ultimate authority has been given to the devil, nor to those who oppose the church's and the gospel's advance.
The fact that evil men exist, and that they do what they can to set up counterfeit "kingdoms," in no way negates nor compromises Christ's full and unique authority. When the church acts on her commission, she is doing what she was created to do.
[Puritan quote of the day: "We are weak, but we are His; we are deformed, but yet carry His image upon us." --Richard Sibbes, in "The Bruised Reed"]