I'm surprised nobody did this before, perhaps because people are more concerned about gameplay reasons than historica.
First of all, this has a historical basis.
(...)
Muslims never historically organized this kind of religion-wide mass holy war after the initial conquests in the same way Christians did.
I like how you are being disagreed with the rationale of "duh, Muslims aren't that overpowered", while the historical argument is being ignored:
You are both obviously not correct.
Muslims indeed did organize something like this. It didn't work exactly like Crusades, that a Caliph declared holy war and used his authority to force other muslim rulers. Simply because Muslim world worked differently.
But there were numerous cases when an emir or any local ruler declared jihad and warriors throughout the muslim world were joining him.
In Anatolia there were the Ghazi warriors organizing religiously justified raids into Byzantine territories... after the creation of Ottoman emirate, encouraged by the Ottomans, who used them to increase their power. Before that something similar happened during muslim expansion to Central Asia. There were numerous such wars in the Sahel where local ruler collected participants from more or less wide spectre of muslim countries and expanded Islam/aimed to reconquer territories ruled by infidels (be them non-muslims or wrong muslims). Most of them were minor and not all of them received caliphal approval, because the caliphal authority didn't really affect major rulers.
Were there no big expeditions like Crusades? I don't think so.
The Almoravids organized large expedition to face the reconquista. So did the Almoravids. So did Saladin. All of them have declared jihads for reconquest of lost lands. They were not caliphs you may object. The Seljuk conquest of Iran was pronounced to be sunni reconquest of Iran ruled by shiite heretics, and as such have received caliphal approval. All of these were joined by warriors from outside of the realm of the main participant, although the forces of the organizer were always very dominant. OTOH, most of actuall crusades (except the most well-known) were very similar to this. So?
We are naturally aware mainly of events as they happened and were described in our cultural world, so your ignorance is understandable and is no shame. But your ignorance of the world outside doesn't mean it didn't exist.