I highly recommend Jonathan Edelstein’s entry at The Head Heeb about the ideology of Christianism. Jonathan develops the concept by analogy to Islamism, and with specific respect to the recently enacted autonomy constitution for Bougainville within Papua New Guinea. But as he notes:
Christianist political threads cuts across denominations and exists in many parts of the world besides the Pacific: the United States, much of eastern and southern Africa, arguably Ireland and Poland. In the Pacific, however, conditions are nearly ideal for Christian-based politics.