This has been running though my head a lot lately. Do all the FE games run though a straight historic line? Or is there multiple timelines a la Zelda? Because obviously some games like the first and Awakening are chronological, as is the "Radiant" games. However, did the events in the Radiant games happen between the first and latest installment for example? I can't quite see how that's possible, unless there are different timelines like mentioned before. Either that or some games happened simultaneously, only on different continents, or perhaps even planets since Tellius (Ike's home land) is said to be one giant landmass akin to Pangea. I wouldn't be surprised if there isn't a definitive answer to this questions, but maybe some of you guys know something about it.

My understanding is that it's more or less like Final Fantasy; many of the games are set in entirely different universes.

Some games are connected and some aren't.
Here's the breakdown:

Akaneian saga
Fire Emblem: Shadow Dragon (DS), Fire Emblem: Heroes of Light and Shadow (DS, fantranslated)... these are the Marth games that are the background mythology for Fire Emblem: Awakening. Both of the DS games are remakes and reremakes of older NES and SNES games.
Fire Emblem: Gaiden (NES, fantranslated) is in this world, but has no bearing on the lore.

Jugdral saga
Fire Emblem: Genealogy of the Holy War, Fire Emblem: Thracia 776 (both SNES, both fantranslated)

Elibe Saga
Fire Emblem (USA, GBA), Fire Emblem: The Binding Blade (GBA, fantranslated)... this is Roy's series

Fire Emblem: Sacred Stones
Totally standalone.

Telius saga
Fire Emblem: Path of Radiance (Gamecube), Fire Emblem: Radiant Dawn (Wii)... this is the Ike series.

Hope that helps!

So basically for example, even if major time travel was possible, Marth would never meet Ike since they live in entirely separate universes. But then that brings up the question as to how you are able to recuit Ike (well okay his "spirit" of sorts) and other non-Akaneian people in Awakening's Outlands area. If there are truly separate universes, then Old Hubba never would have heard of them. Of course that notion could easily just be deemed irrelevant to the main plot, but it does beg the question nonetheless.

Akaneian prehistory and the Halidom of Ylisse are, for our purposes, "Fire Emblem Prime" and the other series are alternate universes. Not alternate timelines, but rather completely separate existences.

The Outlands Gate is alot like the plot device of the show "Sliders". A vortex that grants access to the alternate universes... not sure why Hubba has access to the gate and no one else, nor do I really grok what the cards are about, but a) i am not done with the game and b) only two map packs have come out so it might (?) be explained.

But in all reality, it is a non-plot related shoehorn to explain away optional DLC map packs that press the fan service button, and as cynical as i would like to say it is... I totally enjoyed watching Alm die... ^__^