[spoiler=long]disclaimer: everything here is my interpretation/analysis of how the FE universe(s) works because i spend way too much time thinking about this
I like to think of FE as all happening in the same universe/planet, mostly because it’s fun to think of links between them. From sources given and implications taken from the games themselves, it isn’t hard to order a few of them (namely Akeania/Jugdral/valencia/awakening); those + potentially elibe as well already form a somewhat coherent timeline. The biggest problem, in my mind, is that on the timescale either given or assumed, it’s questionable whether Chrom would be aware of all the legends (particularly that of Ike, if you put Tellius first). It is a fact that the tales of Akaenia, Valencia and Ylisse happen in the same world, two thousand years apart. This much is made explicit by the games themselves. Additionally, developer’s commentary reveals that the Holy War of Jugdral takes place in some unspecified “distant past” before Marth’s war begins, but in the same world. This, combined with the fact that Marth is aware of Anri but not of Sigurd implies that the crusades in Jugdral either took place long before Anri, or on a different continent entirely. More on this later. This already leaves us with FE4G1 -> FE5 -> FE4G2 -> FE1 -> FE2 -> FE3 -> FE13.
Next, let’s talk about Elibe. Elibe is probably the one that was the most difficult for me (yes, even moreso than Magvel), as it introduces the most inconsistencies if we give it the obvious place on the timeline (that is, an alternate world to Marth’s). My first thought was the same as most everyone else’s in here’s - that Elibe is some kind of alternate world (or even an alternate future, if you want to put a diverging timeline in here somewhere), connected via the Dragon’s Gate. The problem with this placement is Chrom. If we assume that Chrom is loosely aware of the events of every previous FE (as legends and such), it would make no sense for Chrom to know of Roy and Lyn as legendary. See, they’re legendary heroes and figures from an alternate future of Chrom’s own world. Even assuming the dragon’s gate remained open (and I see no reason it wouldn’t), it doesn’t make sense for Chrom to know of legends and tales from a world that he would presumably never have any interaction with. So this puts Elibe back onto the main timeline, which conflicts with the whole “dragons and men making peace” deal that akaenia has going on. There also just isn’t enough time between FE1 and FE13 for something as major as the Ending Winter to happen without it being made note of (well, I guess there is, but it most likely couldn’t have happened after the first exalt became a thing because that’s actually in “recent” history for FE13). So the only real place to put Elibe would be before FE1 somewhere. When exactly is pretty arbitrary and you could probably justify putting it anywhere but I chose to put it before FE4.
I’ll be the first to admit that my version of events is pretty hacked together and graspy, but I like it. This section of the timeline begins with the “golden age of dragons”, or the rule of the divine dragons in Akaenia. This is the “dragons and men lived in peace” of FE7’s opening scene. According to the unified timeline of Jugdral/Akaenia/Valencia, there is about three thousand years before the decline of the dragons as described. This decline seems to match the description of the Ending Winter in FE6, so let’s run with that: The Scouring took place because a group of humans decided to rebel against the ruling class of dragons in Elibe and used some kind of ancient voodoo magic to forge the Eight Heroes’ weapons. This took place worldwide, causing the Ending Winter to occur, which had the side effect of severely weakening the divine dragons. The Scouring also forced some (but not all! it is a fact that some dragons remained behind, namely arcadia) the dragons through the Dragon’s Gate. Fast-forward to roughly the beginning of the Lopt Empire. If we assume that the Dragons Gate links Elibe and Akaenia as some kind of portal in the same world (I’m aware they mention it being “another world”, but without extended flight/etc that could just as well mean a sufficiently distant continent), we can place FE7/FE6 right around here. With all the dragons gone from Elibe, humans there would have built up their own civilization, but not necessarily have built up enough to be aware of other continents (namely Akaenia). Most of my reasoning here comes from consideration and modification of this theory, which states that Nils becomes the dragon known as Forseti in the Miracle of Darna. If we place the events of FE7 as roughly contemporary with the early-middle years of the Loptyr Empire (for that matter, you could probably place it at the end), that leaves enough time for Nils to grow older and become powerful enough to bless a wind tome with his power. The rest of my reasoning from here would be an echo of that topic (both the OP and other comments in the thread), so I won’t bother typing it out, but that leads into FE6, then into FE4, etc etc.
Next up is Tellius, which is kind of a bitch to place for the exact opposite reason as Elibe’s. Elibe for me was difficult to place because there were too many significant events for me to fit it into an existing timeline. Tellius, on the other hand, has almost no connections whatsoever with the current timeline, except for really minor hints like the tale of naesala and leanne mentioned by one of the Taguel (was it Yarne?). Oh, and the very existance of Priam, I suppose. I have two theories that I flip-flop between (both of them have inconsistencies but I have no idea how to reconcile them).
The major deciding factor is whether we trust the goddesses’ word that everything was wiped out by the flood. If we do, that necessitates that Tellius come way, way, waaaaaaaaay before anything else we already have (or after, but then we introduce time travelling descendants into the equation, which awakening clearly handled so well). This would begin our timeline with the Great Flood (well, it would start with Ashenura but that’s irrelevant). It would have to be significantly before anything else, because, with everything gone, it would take thousands if not millions of years for the floodwaters to recede enough to have new land (I assume we have some goddess speeding things up a bit). This fits in nicely with our current timeline thus far - The dragon laguz will become the “divine dragons” as described in our lore. I can only assume that they eventually branched into more dragon types than red/white/black because evolution can do that to you. The other laguz types are presumably also affected by the Ending Winter and are forced to evolve into taguel. It’s also made explicit that Ike leaves for lands unknown, which opens the possibility of the rest of the continent going as well (leading to dragon/human populations on what would eventually ebcome elibe/akaenia/jugdral/valencia). A major flaw with this theory for me is that by now we’re reaching over ten thousand years before Chrom (2k between chrom and marth, 4k between marth and golden age of dragons, call it 5k years for the floodwaters to recede… that’s 11k years right there). Chrom even being aware of the Radiant Hero of the Blue Flames is the biggest problem (how many mythical figures do you know from eleven thousand years ago?), that can be handwaved with “killing a goddess is kind of important” and “legends are better-kept in the FE world”.
Option two is that the goddesses were just wrong when they said the flood wiped out everything. Yune said themselves that they aren’t perfect, meaning they aren’t omnipotent and wouldn’t necessarily know about other parts of the world. This gives us a lot more flexibility with where we put Tellius on our timeline. I like to put the Ending Winter as the cause of the Great Flood, mostly because it pleases me when things line up. Consider this - Yune and Ashera aren’t even aware of the other continents. What if they simply aren’t as powerful as they think they are and the flood was a combination of Yune going nuts and an external force of nature. Or even, Yune went nuts because of an external natural disruption. Either one works, I don’t really care. Regardless, this puts the events of FE9 roughly contemporary with the establishment of the Granbell republic. The rest of the events are largely irrelevant (Ike still leaves, a lot of what I said about Laguz etc still holds, except laguz probably became taguel or died out entirely for other reasons… don’t ask me).
The only other inconsistency with both placements is the fact that Priam matters. You could put Ike literally anywhere from the birth of the world to the first exalt and it still wouldn’t make sense for people to care that Priam is his descendant (imagine me saying “hey i’m descended from genghis khan and alexander the great” - not super convincing and nobody really cares). Unfortunately I don’t know how to deal with that as the onlyl real way would be to put FE10 after the first exalt which is patently ridiculous.
Magvel I just kind of stuffed arbitrarily as contemporary with the first exalt. Literally the only thing we have to go on is that manaketes exist and are extremely rare, which would mean it’s long past the Ending Winter. You could put it almost literally anywhere and it wouldn’t matter. I have a headcanon that Formortiis is a servant of Grima, but I have no particular backing for that theory. They’re both just evil for the sake of it I suppose?
I think that covers just about everything of note (either legitimately worked in, handwaved or explicitly ignored)… Oh the outrealms are a thing but as far as i’m concerned those are hubba’s bedroom chambers that he alters with the same voodoo magic that einherjar are made out of
this is sitting on a file on my desktop because it took three hours to write and fuck FE plot