In the late Roman period and the early Middle Ages, Germanic people were becoming Christianized. The process of Christianization was a top down process and it was one that both helped and hindered the German people's political development.
The German people tended to move to Christianity along with their leaders. Leaders typically converted out of a belief that Christianity would make them and their people stronger.
The main problem with German conversion to Christianity was that they converted to the "wrong" sort of Christianity. The Germans became Arian (not Aryan) Christians. This was a problem when they tried to rule in former Roman areas because the people there were Catholic.
It was not until Clovis converted to Catholicism that this problem went away. When Clovis converted to Catholicism, it helped to create the first really strong Germanic kingdom. Since Clovis had the support of the Church, he was helped in his attempts to conquer and maintain an empire.
Thus, conversion to Christianity had an impact on the development of German kingdoms during the early Middle Ages.