I have a few ideas about how to improve the religions system...
1. Minor religions:
Historically, there were many well known religions whose followers were a minority in their countries.
These religions did not have any diplomatic effect, but they had a good cultural effect.
For example: Jainism, Rastafari, Sikhism, Bahai faith, Yarsanism, Shenism, or maybe Gnosticism..
So is there a possibility to mod this like this(?):
A minor religion can't become a state religion.
A minor religion doesn't have monasteries or cathedrals. Only a temple, and a wonder in its holy city.
A minor religion can't build missionaries. It spreads only naturally.
But they all have the same cultural bonuses.
2. Cities start with a religion:
One thing that realy annoys me is that when a city is founded it usually starts without any religion.
It looks a bit weird that by the year 1400 AD I found religionless cities, even if it is in the most cultural area of the world!
Think about it... the settlers have origins... they don't creat a new culture...
So my idea is that when a city is founded, it starts with one of the religions that have been in the city where the settlers originally came from.
It just makes more sense. Because many times I have a chaos of religions in my civilization, and in every new city I found a different religion is spread.
I'm sure im not the only one noticing that.
* You can also make it a bit different in every civic.
For example, in Theocracy a city can only start with the state religion (unless the settler's original city doesn't have the state religion..).
In Organaised Religion a city has a 70% rate of starting with the state religion, and 30% of starting with any other religion from the settler's original city.
In Free Religion it randomally generates one of the original city's religions.
* If a religion is spread in a city right after completing the creation of a settler, that religion wouldn't be able to be the starting religion of the new city that the settlers will find.
3. Ancient pagan religion:
Since the dawn of civilizations, before the well-known religions were founded, people all around the world did have religions.
They weren't firmly established in the society, but diplomatically they were very important.
So I think it should be inculded in the game:
- Every civilization's first city starts with the Pagan religion, and with Paganism as the state religion.
- If you build settlers in a Pagan city, (according to the 2nd idea) the new city they will found will be Pagan.
- If a religion is spread in a Pagan city, the Paganism will disappear from the city in a few years (Depends on how many Pagan buildings are in the city, and how cultural is the city).
- Two Pagan civilizations won't have a relations boost due to their religious similarity. Because throught the history there have been hundreds of different Pagan religions.
But the relationship between a Pagan civilization and a regular religion civilization will be similiar to the relationship between any two civilizations with differrent religions (the same penalty).
-If Paganism disappears from a city, the Pagan buildings will not disappear. They will still have a cultural effect, but they will cause +1 unhappiness.
A good idea is adding a new function to inquisitors - destroy Pagan buildings.
- No Pagan missionaries. Not because of an historical reason.
Just because every city which is not Pagan must have other religions already, so actually Paganism can not be spread.
That will also help Paganism disappear from the world by the time it needs to disappear.
- Paganism does not have a holy city, nor a wonder.
- I haven't thought about monasteries yet.
- Barbarians start with Paganism too.
The goal is to make Paganism disappear from the central civilizations around the beginning of the medival era, but until then, to improve the religions system in the game.