It remains the most important of Pacelli's concordats. There have been three separate waves of concordats. Pius concluded some thirty concordats and State treaties during his pontificate. The concordats and agreements also regulate public school catechisms and military chaplains. I era saw the greatest proliferation of concordats in history. There have been at least several hundred concordats over the centuries. Pius's major diplomatic approach was to make concordats. Pius XI's major diplomatic approach was to make concordats. In modern concordats Rome has repeatedly granted the right of patronage to Protestant princes. The concordats were generally observed by the countries involved, with the exception of Germany. Concordats began during the First Crusade's end in 1098. Concordats are revocable when they redound to the serious injury of the Church. As Cardinal Secretary of State, Pacelli signed concordats with a number of countries and states.