[ink.] History Problem of the Week 13/9

Hi comrades! I'm the Prophet, and I'll be publishing weekly history problems from today on. These problems require you to recognize a specific historical event, figure, or concept based on a series of descriptions. Without any further ado, let's begin with our first [ink.] History Problem of the Week!

Guess a War!

1. This war was initially called by the Pope in the name of God. Yet, his Holiness later excommunicated all participants on the offensive side after capturing a crucial port on the coast of the Adriatic Sea.

2. The intent of the war was to conquer a Holy site of Christianity. However, a series of events culminated in the fall and sack of "the City of World's Desire."

3. The outcome of the war contributed to the decline and fall of the Byzantine Empire, on the ruins of which the victors of the war established a number of French or Italian states.

4. This war has solidified a schism between two branches of the same religion.

Take a guess!

Remember to post your answer in the comment section. It doesn't matter if you get it right or wrong, as there might be multiple plausible answers to the question!