No one joins my faction for independence.

[Extraordinarily Mature Slav]

I am currently playing as the King of Serbia under the Byzantine Empire, I am trying to gather people to start a war for independence. Though I've had my faction up for about 10+ years no one has joined, with an empire as big as the Byzantine Empire (with multiple Liberty Wars every other liege.) there should be lots of vassals willing to join my faction. I make up about 45% of the military needed to match the Byzantines, so I don't need many more fellow vassals to join.

[BaCaz]

Best advice I can give you is this:
Build up your military power as much as possible, and when you have more than 50% of their power you either time your demand with a natural succession or you force a succession by murder, and when the new Emporer is weakened from the succession possibly fighting a Liberty war you push your demand. You can use mercs to get you the rest of the way if you have the money for it.

[dwarfpcfan]

murder the current emperor, watch his heir take over and get sucker punched in the face by the short reign penalties and multiple vassals turning on him

[Extraordinarily Mature Slav]

Kekw, the Emperor died, and all that happened was 1 dude from Nubia joined my faction, still only had 50%.

[LzDK14]

You DON'T need help to make a demand in faction.
So...
1. Get Intrigue Truth is relative perk.
2. Fabricate hook on your liege, or aquire hook in any other way.
3. Modify your contract to enable Concil rights option or demand a position of a spymaster with hook.
4. Get Kidnapper Intrigue perk
5. Abduct your liege.
6. Demand independence.
7. Instawin independence war.
8. ???
9. Enjoy.