Christianity is not liberal democracy.
As for Christian nationalism, it was pioneered by Lutherans.
The following excerpt comes from Eric W. Gritsch’s book A History of Lutheranism:
“Lutheranism spread in the north and east of Germany; Catholicism remained entrenched in the south and west. “The Reformation,” as the age of sixteenth-century reform became known, ended in `1555 with a compromise between Lutheran and Catholic territories. The territorial imperative, well known in the world of animals, had its way in the world of human politics. But humans created a complex bureaucracy when a territory is ruled by uniformity in all phases of life. An ecclesiastical hierarchy quickly developed parallel to the secular one; both were controlled by the territorial ruler. He quickly appointed officials in the church headed by a superintendent (formerly bishop) who chaired a consistory (in Wittenberg) or a church council (in Württemberg). There was no freedom of conscience, as Luther had advocated at Worms in 1521. Territorial uniformity only permitted one set of doctrines, one form of public worship, and one specific morality created by the officials of church and state. The territorial prince had veto power in all phases of life in his territory. Lutheran territories tended to be more absolutist, indeed autocratic, than Catholic ones, perhaps because Catholic rulers belonged to a worldwide church with more room for deliberations, despite the strong arm of Rome …
But confessional territorial rule kept Lutheranism tied to the medieval concept of “Christendom,” that is, the fusion of church and state …”
The following excerpt comes from Perez Zagorin’s book How the Idea of Religious Toleration Came to the West.
“For Luther, as for his medieval Catholic predecessors, religious unity presupposed that Christian society and the church must be coterminous. It is therefore not surprising that in the German lands that became Protestant under Lutheran influence, and where the prince replaced the pope and ecclesiastical hierarchy in the control and supervision of the church, all Christians were required to belong to the latter as the only religious body recognized by the state. This principle was enshrined in the Peace of Augsburg of 1555. …”
There was one religion, one culture and one morality in most of Northern Europe after the Reformation. It was Lutheranism which was the established church in the German states, Scandinavia and Iceland. Lutheran princes and kings played a large role in the life of the church in all Lutheran territories.