Why was the Holy Roman Empire forced to seek peace with the Lutheran princes?

The Holy Roman Empire seek peace with the Lutheran Princes because of the political and religous problem arising in the Holy Roman Empire. The rulers within the empire where constantly at war. They were struggling to keep their territories. Aside from that, Protestantism started to emerge. King Charles V, the Holy Emperor of Rome, tried to fight off Protestantism Reformation by making Counter-Reformation hoping to stop the spreading of Protestantism. As a sign of peace, King Charles V, he signed the Peace of Ausburg or Ausburg Settlement with the Lutheran princes