There's no apparent chronology outside of Disgaea 1, Disgaea D2 (Disgaea's direct sequel) Disgaea 2 (an apparent, sort of sequel). As you'll learn there are many, many alternate Netherworlds (and quite possibly different timelines). When Laharl, Etna and the gang visit future games they're generally doing so from an "alternate" netherworld to whichever world your protagonist happens to inhabit.
But for what it's worth [Disgaea endgame spoilers]
In the first Disgaea in the "Good" ending Flonne becomes a Fallen Angel, hence her existence as a Fallen Angel in most other games. I don't believe a reason is ever given for Flonne's sudden appearance as Archangel either.
Due to the above spoiler and various quotes from the Disgaea 1 characters (such as Laharl complaining about not being the main character in Disgaea 3) it does seem that Disgaea 1 happened before all other games and/or Laharl, Etna and Flonne show up in the other Netherworlds after the events of the first Disgaea.
Due to the reappearances of main characters as bonus/DLC characters in each successive generation it can be roughly assumed each game happens after the previously released games, however the remakes confuse this issue even more; certain Disgaea 3 characters now exist in Disaea 2 Dark Hero Days. But the Chronology is largely irrelevant outside of Disgaea 1/2/D2 if you consider postgame content to be non-cannon (since postgame + bonus characters is at best a time paradox/alternate universe funtime in most games), since Disgaea 3 and 4's stories exist completely separate of the D1/2 worlds.
I've only played the games and read the Disgaea 1/2 mangas though; I'm not sure what extended universe material is considered cannon or what material might give clues to the chronology.