* A completely overhauled factions system -- rather than solely having factions which go to war with their liege as soon as they are strong enough, there are also "common interest" factions which consist of vassals who meet regularly and can reward a liege who's kept them happy or make demands of a liege with whom they're angry...and who can start a civil war if their liege doesn't comply. These civil wars can be incredibly dangerous, as other factions can join in the war if the liege is unpopular. More information on how these factions work is available here.



* Catholic and Orthodox religions are united as Chalcedonian Christianity in the Old Gods and Charlemagne bookmarks. The schism only occurs after the millenium if the right events occur prior to that, and can be prevented should a Patriarch Supreme be anointed.



* A cadet system for younger brothers of very large dynasties to establish their own dynasties if they should ever inherit a title. Likewise, powerful rulers who are part of very large dynasties but who not the head of that dynasty (and not closely related to him) may elect to start their own -- particularly if they are Muslim, who will always start their own dynasty if not in the realm of thier dynasty head.



* Overhauled heresies -- conversion to heresies is not completely random, and sometimes "heretics" will actually switch to non-heretic religions within the same religion group (where it makes sense). There are brand new heresies, such as the Adoptionists and Tondrakians (amongst others), and many individual heresies have been given a great deal of unique content to make them more interesting to play.



* A more logical system for adventurers -- adventurers will travel around to nearby kingdoms, attempting to raise money from sympathetic rulers and by campaigning in lands. Only if they raise sufficient funds will they be able to form a host, and the size of the host will depend on the amount of coin they raised as well as their individual prowess. A deceptive ruler may attempt to take their captive when they arrive and offer you them to you in exchange for a hefty ransom.



* A coronation system, which requires feudal kings and emperors to hold a coronation -- an event which invites not only vassals but nearby independent rulers and relatives -- which will solidify their rule. Until they are coronated, weak claims can be enforced against them and their Crown Authority can not be increased.



* A Spy Network rating, built by assigning the Spymaster to the Build Spy Network job. Spy Network can be spent to speed up the success of plots, and can also be spent to hire an assassin to target someone you have a murder plot against. The rating slows down plots against you, but you can devote your own Spy Network to reducing your target's.



* The vanilla decadence system for Muslims is gone -- mostly. Muslims can still gain the Decadent trait, and if they are in the realm of the head of their dynasty, they can cause him to gain a "Decadent Dynasty" trait of increasing levels of negative opinion with other Muslims based on how many family members have the trait. The dynasty head can demand they straighten up if he has enough Piety, and should they refuse he gets the right to exile (not execute) them. An exiled decadent family member can be almost as much trouble away as in the realm, as they will otherwise plot and scheme and ask for money and estates.



* A system for Martyrs and Saints. Christians who die during a Crusade or executed by an infidel may become Martyrs. Rulers who die with very high Piety (or with other qualifications, such as being a Martyr or having mended the Schism) may be declared Saints -- this changes the portrait and provides Piety to their family.



* Tribal rulers feudalize similar to the pre-Horse Lords manner -- they must upgrade their capital holding's hillfort or market city, and must have Absolute Tribal Organization. Their non-upgraded holdings do not turn into castles, but can be once they're upgraded, and they do not instantly get cities and temples in every province. Cities and temples can be built prior to feudalization, with difficulty, and that process speeds up for the first century after feudalization in provinces of the ruler's culture.



* A new tyranny system similar to EU: Rome. Kings cannot wantonly revoke titles, imprison, banish or execute subjects any more without incurring Tyranny. The "Tyrant" trait lowers relationships with everyone and in turn makes it more likely for vassals to revolt, and sufficiently high tyranny can cause a "dynastic stain" which is passed on to descendants.



* A unique map with many more provinces and territories, along with a revamped setup for de jure kingdoms and empires. One thing experienced players will immediately notice is the scarcity of de jure empires -- most empires are formed as titular titles first, and gain de jure territory through the course of the game.



* A revamped system of demesne laws. Crown Authority has also been changed, having the effects of the vanilla Centralization law folded into it while simultaneously making it more difficult to raise (requiring a certain prestige score). Kingdoms and empires require a medium level of Crown Authority in order to enforce their de jure claims.



* Changing of Crusade/Jihad mechanics to more accurately and fairly represent large-scale holy wars. Winning a crusade/jihad results in the de jure kingdom of the war's target being created (e.g.: a successful Crusade for Jerusalem results in the Kingdom of Jerusalem being created and awarded to the victor), as well as the institution of a special truce to help Crusader states survive more than a few years.



* All Christian religions have the capability to unite Christianity -- whether it be via Mending the Schism (for Catholics and Orthodox), Repudiating the Council of Chalcedon (for Miaphysites) or Repudiating the Council of Ephesus (for Nestorians). This only requires that the religion has a religion head, and works even if the "main" religion has been replaced with a heresy.



* The episcopal sees (Rome, Constantinople, Jerusalem, Antioch, Alexandria) have ducal patriarchate titles which are gained when a Catholic or autocephaly religion (like Orthodox) gains the temple barony. For autocephaly religions, it's this title which constitutes the actual pentarchy...and some religions (like Miaphysites or Nestorians) only gain the Petrine sees and not Rome or Jerusalem.



* Adds a greater list of ambitions and plots, including: "Get a lover", "Break out of prison", "convert a province", "win a war", etc.



* A completely revamped set-up for the historical transition between Charlemagne and the Carolingian Empire to the Holy Roman Empire, with events allowing for this to occur even with the AI at the helm (or in a completely ahistorical manner). The de jure set-up for the Holy Roman Empire has also changed, with the former kingdom of Germany broken up into its individual "stem duchies" while under Holy Roman rule.



* Expanded mechanics for female heirs and rulers. Women can now have their claims enforced by war even on agnatic titles, can have a martial trait which allows them to lead armies (though only in certain cultures, or at certain levels of gender law), and have special versions of some events (such as hunting and tournaments) which apply only to them.



* Changing succession laws requires prestige, and can cause anger not only among your vassals but particularly among those who find themselves disinherited as a result of the change. Some laws, like Feudal Elective or Tanistry, require the agreement of your vassals in order to change them at all.



* While tribal rulers cannot build new holdings normally, they will have pious characters sometimes ask to found a temple with their support. Their steward may also use the "Settle Tribe" ability in provinces of their culture to find a site for a new city -- which will require support and many years to build.



* The ability to disinherit an heir -- though an angry former heir may take arms against you, if he can find support.



* Expanded events for pagans, including new pagan religions such as Celtic and Ancient Egyptian -- many of which were adapted from the Ancient Religions mod.



* A "Shattered Realm" function, usable at the beginning of any game, which allows you to break up every kingdom or even duchy in the world and start everyone at the same level. It also has a function which allows you to change the world's starting religion set-up, making pagans dominant in many areas and all but removing Christianity entirely.



* Many new additional start dates, focusing on characters and periods throughout the era.



* A host of improvements for the AI, insofar as how they run their realms and how they use the existing events and wars a little more intelligently.



* A myriad of other new events and decisions, many of which are too minor to list here and also many of which are fixes for vanilla bugs or revisions of vanilla events & decisions to improve their function in the game.