From the Conclusion to Part I – Empires in Scripture:

God’s empire is founded on the self-sacrificial death of Jesus and of the firstfruits of His people. It is renewed by ritual commemoration of Jesus in Eucharist, which forms a community readied for martyrdom [Leithart uses this term in its original sense of “witness”]. God’s empire is not a transhistorical aspiration, an ideal, or a sentiment of fellow feeling among nations. It takes concrete form in a catholic church, where rival rulers and emperors, rival nations and empires, become table fellows and, under the church’s discipline learn the Lord’s ways of peace and justice. Under Jesus and filled with the pentecostal Spirit, the ecclesial empire is a historical form of international community. The church is the eschatological empire already founded (52).

 From the Conclusion to Part II – Americanism:

Checks and balances among the branches of the federal government are an inadequate guarantor of liberty. No American church is allowed to become independent or powerful enough to challenge American policy effectively; few try. . . . When was the last time an American politician was excommunicated? When was the last time an excommunication had any effect on American politics? . . . Individual Christians do not have the virtues necessary to function as citizens of God’s imperium because American churches have discipled them to function as citizens of the American imperium instead (111).