ok here's an example. I call it Narmox's Patented Dynamic Unique Units Tech Tree
Let's say you want sortof unique units, but don't want to predetermine them in advance. You also want the civilization to be able to choose its unique unit, but not have access to other unique units once they chose one.
So you want to tech tree to be like "If you discover Legionaries, you cannot research Immortals, and vice versa".
Another example: Looking at Teturkhan's Test of Time map&mod, you'll see that different civilizations have different research paths. To accomplish this, Teturkhan had to fudge things a bit by giving these civs hidden starting techs that other techs would depend on, hence locking christian civs to christian techs, american civs to american techs, etc.
This could be made more dynamic though! IF you want christians and muslims to have slightly different tech trees, but you don't want to decide in advance who's christian and who's muslim, then the idea we're discussing works. "If you know Christianity, then you have access to this this and this, but not those techs." Same thing for other religions.
Let's take another example, with a lord of the rings mods. Early on you could have the chance to join the alliance of elves and humans, or mordor, or to be neutral.. The choice could be made with a tech too - thus giving you access to a different tech path depending on which alignment you chose!
I hope this clears it up a bit
Hm ok I just reread the posts above discussing this, and my examples are just SLIGHTLY different. But only slightly
