I put in the spoilers warning just in case. So here goes.

As i was downloading some music from the newer FF games i decided to go to Wikipedia and look up some info on each. I discovered that some of the newer games like Type-0, Nova Crystalis, etc. all have similar themes such as l'cie and Fal'Cie. As i read each article i began to see a history timeline and i remembered all of the miscellaneous hints to what happened in the past on Gran Pulse in FF13. It seems that there is a subtle connection to the new games and the unknown history of what happened between Pulse and Cocoon centuries ago.

It seems that a god defeated his own mother and then took over her creations as his own. Fearing some kind of karmic retribution he created the first Fal'Cie to watch over the world and humanity. These Fal'Cie also created their own Fal'Cie to help guide humanity and take care of Cocoon, turning it into a paradise for humanity. Barthandelus of FF13 makes a number of mentions as to the gods abandoning Cocoon and Pulse and that only a sacrifice can awaken the gods because the sudden death of so many would case the gods to stir. There are a number of other points as well but i think I'll leave then to you to investigate so i don't spoil it all, but it seems that in the context of a timeline, if we can argue that there is one, that FF13-2 is actually the last 'event' in the Final Fantasy Fabula Nova Crystallis collection timeline. I'll leave the link to the wikipedia article to make things easier.

http://en.wikipedia.org/wiki/Fabula_Nova_Crystallis_Final_Fantasy

As far as I was aware each title in the Fabula Nova Crystalis games (which FFXIII and XIII-2 are a part of) aren't actually all set on the same world, but rather just share common themes - namely, the 'i'cie/fal'cie/focus' idea. Other than that, each game is set in it's own unique world with different characters and story lines.

To be honest, I don't even know exactly why Square Enix decided on doing a compilation in this way, (personally I would just wish they'd stop this whole stupid 'compilation whoring' plan and just concentrate on making standalone FF titles), as the connecting theme between each title is tenuous at best.

I think the games are connected. But Square and other companies are notorious for claiming there is no connection when there obviously is, XenoSaga ring any bells? Now as far as compilations go i can see why Square is doing this. Its time to do something different, see if it works, try something new. Complacency breeds stagnation in business and the Final Fantasy series is a business so they have to try something new not only for revenues sake but also to keep ideas fresh and keep the fans interested.