R5: Playing tall as the custom Empire of Sicily, I sent the chinese emperor two emerald tablets to smash the Seljuks (who controlled more or less everything east of anatolia), and the HRE (which recently conquered France and thus held everything between Poland and Mauretania).

Getting the Chinese involved was just a formality in both cases. I can raise 50k troops from my demesne, and occupying holdings gives like 10% warscore each.

I have the republics of Sardinia and Jerusalem as vassals for that sweet cash (monthly income of 160 gold or so, of which 40% is from city tax), but other than that I've been trying to set up crusader states, as it were, conquering stuff in holy war, giving it to a good candidate and granting them independence, supporting them as needed. I occasionally forget about them, so right now, it's just Alexandria and the Byzantine Empire that are more or less my client states.