I've got a question.

[Derfasciti]

This entire section seems to be a collection of alternate history scenarios. If this is so, how do I participate and what do I need to know?

[Flavius Clemens]

Yes, that's the whole idea of the Chapter House, the idea began with the original IH 3 by Kraxis (numbers 1 and 2 were done on a different site) and they've been so popular that they got their own section.

Each new history runs on its own variation on the general theme, some are open to all posters, others - e.g. 17th Century - have specific roles for individual posters, and need you to register as a particular role to join in.

Of the ones active at the moment, Kraxis' Dual of the Sea is nearing it's climax. We are playing the German fleet with decisions taken by a majority of replies made between Kraxis posting a set of questions and the time he starts writing up the next chapter. Another site is playing our Royal Navy opponents. Red Flood and La-Florida run on a similar basis, but only have one side, everything else is referee controlled. 17th C has its own set of rules detailed in that thread (I'm not sure if this is still taking new players).

If you want to join in one I suggest reading through the story to date to get the general feel of the story and how it's running, and then join in when you feel you can contribute. Obviously it helps to have some background knowledge of the period the history is set in, but you don't need to be an expert up front you can learn more as you go along. But be warned, they can be addictive, and you may find yourself pouring over Wikkipedia etc for ages getting background on the decisions you're taking !

[Derfasciti]

Ah, so at least for some of them, you can just put in your two cents on the specific question and the votes are tallied and majority rules?

How/who/what determines the end of the scenario?

[Franconicus]

The creator of the stoty makes the rules. We had stories where the first or the third vote counted. Today, the mojority vote is most popular.

[Kraxis]

Everyone can leave a post in the open stories with choices.

However, it is generally a good idea to make an argument for the choice (if for nothing else than to prove you are serious and not just nuking the story).

First post decisions (where the first poster gets the choice) is good for faster paced stories with few choices for each chapter. It gives the readers a sense of urgency, which might cause them to slip a bit and make bad choices as they scramble to be the first (their choice is the right one after all, and it is important that it is chosen).
However, it also leads to a relatively stagnant thread in between the author posting and the choice is made. There is little need to post as it can't really affect the path taken. Hence the speed. Also the urgency can lead to contradictory choices picked in successive chapters.
Take a look at Interactive History III: Antiochus' Dilemma (https://forums.totalwar.org/vb/showthread.php?t=50702) for a good insight to this.

The majority decision stories can on the other hand grow immensively, and can drain the author, as he needs to take in all the choices, opinions and ideas. Also at times there are ties. Further, with multiple choices you can end up with odd combinations as the most posters haven't got the same idea of what is right (if people are too much in agreement I consider the choices to have been bad on my part).