"Since Jesus' ascension, the kingdom of God is the work of God through his people, Bringing Jesus' kingship to bear on the whole world. It is bringing people to bow the knee to him, and every tongue to confess his lordship. It is turning people into disciples, baptizing, and teaching them to observe everything that Jesus has taught us. Note that our teaching is not just any "teaching" (didasko), but a teaching "to observe" (tereo). The focus is not on propositions, but on actions. The discipleship class leads not only to "knowing that," but "knowing how." Insofar as the teaching remains at the intellectual level, the work is not done. The teaching is to be kept, observed, applied." - Frame, ST, p93.
Christ's ascension did not relegate His reign to over the church only. In fact, it declared His kingship over all of His creation. He is the God-man set upon the throne to rule over all of heaven and earth.