Caliphate System

Muslim nations have the ability to compete for leadership of Islam by proclaiming their leader as the Caliph.

Muslim nations that have rival claims to the Caliphate get access to special CB and War Goals. When a rival defeats another in a war the defeated rival gains a 'claim to Caliphate Rebuked' modifier which prevents them from taking additional Caliphate missions, events and decision for a period of time.

Sunni rulers can declare themselves as the Caliph at will once they meet the requirements.
Shia leaders must first go through a process where they are either determined to be descended from the Prophet or not. If not they have the option of marrying a descendant and allowing their heir the opportunity to declare themselves as the Caliph.

Declaring a ruler as the rightful Caliph and being able to hold that title (not being defeated by a rival) is a requirement to enacting the Unify Islam Decision

Unify Islam bonuses are now:
stability_cost_modifier = -0.5
global_missionary_strength = 0.5
tolerance_own = 5
tolerance_heretic = 3
land_morale = 0.2

I think this is a better reflection of the value of a unified Caliphate. It was able to expand quickly because of the fervor of the newly converted - expressed here as stability, lack of unrest and land morale.

Middle Kingdom Tribute System

This event system attempts to provide some of the flavor of the Tribute System practiced by the Ming and Qing dynasties. The mod portrays the system as key component of the international system in East Asia. There is a larger, powerful hegemon (Ming at the campaign start) that attempts to get neighboring nations to agree to a very weak form of suzerainty in exchange for good relations, trading rights and domestic legitimacy. The mod tries to capture the political, economic social aspects of the system and present viable options that would induce both the hegemon and the smaller states to take part in the system.

To become the Tribute System Hegemon a state much meet these conditions:
Total development 500 or Government rank of Empire
Have a capital in the Mongolia, Manchuria, Tibet, North China, South China, Japan, Xinan, Moluccas or Indo China areas.
Have taken a Strategic Decision to form China, Manchu, Great Mongol Empire, Japan, Tibet, Korea, Malaya, Burma, Shan, or the geographic based Empire
Not have a Strategic Decision Rebuked modifier
Have a balance neutral or positive war record against other major powers (mod designated rivals)
Be the strongest trade power in the Girin, Lhasa, Chengdu, Canton, Nippon, Hangzhou, Xian, Beijing, Philippines, Moluccas, Gulf of Siam or Yumen trade notes

Once a hegemon has declared themselves as the Son of Heaven and created the Tribute System, an event fires which asks all valid nations to join the system. States have about a 70-30 chance of joining the system which skews more likely if the hegemon is much stronger militarily.

States are asked to join the system if they meet these conditions:
Do no claim to be Son of Heaven
Ruler has not previously joined Tribute System (this is a ruler flag and thus clears with each new ruler)
Ruler has not previously refused to join Tribute System (this is a ruler flag and thus clears with each new ruler)
Have a capital in the Mongolia, Manchuria, Tibet, North China, South China, Japan, Xinan, Moluccas or Indo China areas.
Have NOT taken a Strategic Decision to form China, Manchu, Great Mongol Empire, Japan, Tibet, Korea, Malaya, Burma, Shan, or the geographic based Empire
Is NOT a subject
Has a merchant in any trade node in which the Hegemon is the strongest trade power (only trade nodes from the hegemon list)

A state will then send a positive or negative reply back to the hegemon

Benefits of joining for the hegemon:
prestige = 1
horde_unity = 0.5
legitimacy = 0.5
devotion = 0.3
republican_tradition = 0.03
global_own_trade_power = 0.25
global_trade_goods_size_modifier = 0.1
global_tax_modifier = 0.15
Add 40% mercantilism
+50 opinion points in relations

Benefits of joining for the state:
horde_unity = 0.5
legitimacy = 0.5
devotion = 0.3
republican_tradition = 0.03
trade_efficiency = 0.1
global_foreign_trade_power = 0.20
trade_range_modifier = 0.20
trade_steering = 0.1
caravan_power = 0.1
+50 opinion points in relations

If the hegemon is defeated by another major power (and then is given the Claim of China Rebuked modifier) then the system disintegrates, reflecting the fact that the hegemon does not have sufficient prestige to support the notion that they rule all under heaven. The hegemon may reinstitute the system once their Rebuked modifier is removed and they have met the other requirements.

If another large state rises in the area, they can declare their ruler as a rival Son of Heaven. Another state can seize control of the Tribute System from the original state if the original state’s system disintegrates due to military defeat.