Complex sentence: In the 11th and 12th centuries, a series of Popes challenged the authority of European monarchies over control of appointments, or investitures, of church officials such as bishops and abbots.
Split into simpler sentences: In the 11th and 12th centuries, a series of Popes challenged the authority of European monarchies. The issue was whether the pope or the monarch would name (investiture) powerful of church officials such as bishops and abbots.