Oh, I get what you mean. I think there is a difference in how games like Total War view and represent history and how Civ4 (or DoC) does. Total War is mostly static historically, and there are no mechanics like technology (correct me if I'm wrong, I left the series behind after Medieval 2) that model historical progression. So instead, it has certain historical events that represent historical developments and somewhat change how the game works.
In DoC, history is more a product of the player's agency (both the human player, and to a lesser degree the AI's). America is there from the start, and once you get the technology to reach it you can decide to go there or not. So in a way, it is up to you to make certain things happen, and to make "historical" things happen.
Obviously, vanilla Civ4 is even more free form than this mod, and you could probably argue that it doesn't try to represent history at all, but only uses history as the theme for its strategy mechanics. So there are a lot of elements added in RFC/DoC that make the game more "historical", but for the most part they are not set events (there are exceptions to this, for example most civs will always spawn regardless of what happens). Instead, there is stuff that happens which is contingent on player behaviour, like the American conquerors Tigranes mentioned. At the same time, the AI is "encouraged" (but not predetermined) to expand / settle / research historically, with some leeway for what that means. The player is not constrained at all, although I also tried to encourage players by other means. For example, winning the Unique Historical Victory generally requires historical behaviour. Usually your civilisation's strengths are chosen in a way that they synergise well with historical play. And so on.
In my personal preference, this vision of history as the consequence of decisions within historical constraints is both more accurate and more interesting and enjoyable than the idea of fixed historical events, and my impression is that most of the DoC community feels the same way. Not that DoC always succeeds in doing justice to these goals (it's harder to do), but I'm trying my best.
TLDR: if the game is boring because of AI inaction, let me know and I'll see what I can do. If it's boring because you're not doing anything or because you have no idea what to do, give the Unique Historical Victories a try: they're usually designed to make you go out of your comfort zone while still doing things that are historically appropriate for your civ.
(Maybe not with Japan though - its UHV is specifically intended to encourage isolation for long parts of the game, and you had that experience already.)