One aspect of the Kingdom of God that we often misunderstand, is that this Kingdom is at war. The Genesis creation story teaches us that God originally created the cosmos as his own domain, and specifically on Earth, he placed his image-bearers as viceroys--rulers in his stead--and stewards of that domain. However, a deceitful enemy tempted humans to disobey their creator, and through a process we describe as "the Fall," seized control of God's good creation. Since that time, through various tactics and strategies, God and those forces loyal to him have been engaged in warfare with the enemy, fighting to retake God's lost territory.
Citizens of God's Kingdom are soldiers in that battle; not with conventional human weapons, but with weapons nonetheless (2 Cor. 10:3-6), pulling down strongholds and taking territory for the Kingdom. But just as our weapons are not of the flesh, the strongholds we attack are not ordinary land territory, but rather "every lofty opinion raised against the knowledge of God" (v. 5), so more subjects of the kingdom of this world, will place themselves in subjection to the True King.
For what we are really trying to do in evangelism, is not to "save souls from hell," but rather to recruit for the resistance! It is when those enslaved to the Powers renounce their allegiance, are freed from their chains, and place their allegiance in the True King, that the Kingdom advances. Those new recruits are naturalized into citizenship in the Kingdom, renounce their former allegiance, and bear new (different) arms for their sovereign King. They, like we, become ambassadors and soldiers of the King, waging war against the Powers by ministering to the Powers' subjects with the paradoxical weapons of love and peace and kindness and justice.
Kingdom citizens, we are living in enemy territory! From the Bible Belt of the United States to the steppes of Siberia to the jungles of Myanmar to the deserts of Saudi Arabia, this world is the territory of the Prince of this world (Lk 4:5-6), and that Prince is the sworn enemy of the Prince of Peace! There is not, never has been, and never will be a Christian nation. The Christian nation, the Kingdom of God, knows no national boundaries, fights no earthly wars, but seeks recruits from all men everywhere to again acknowledge and serve the one God and his anointed king, Jesus Christ.