Here's where I'm at with my ST narrative theory (informed by what we know and can infer from what's been released):
At the time of TFA...
- After ROTJ, the Empire's control over the galaxy collapses but its power-base refuses to surrender outright to the Alliance.
- Between ROTJ and TFA, there has been a power struggle within the ranks of the Imperial Military keeping the threat of a large-scale war in check. However, there has been state of cold war between the emerging "New Republic" and the "Imperial Remnant" due to the size of the Empire's forces and systems that remain loyal to it, and skirmishes have arisen from time to time.
The Force, our leads, the Sith, etc:
- Post ROTJ, Luke attempts to establish a New Jedi Order but fears that he could disrupt the "balance" that was created by Anakin's sacrifice. Believing the galaxy was experiencing its first peace in decades, Luke retreats into isolation where he can study the Force and prevent the galaxy from plunging into further chaos from Jedi-Sith-related conflict. He decides that the dogma of the Jedi Order was just as much responsible for the Clone Wars and galactic conflict as the Sith.
- Leia becomes leader of the New Republic and Han is a general of the Republic Forces. They marry and have a son (Adam Driver) and daughter (Rey). Leia and Luke decide that their children should not be trained in the Force for reasons described.
Why a ST exists...
- While the Republic has put a premium on forging peace and establishing a new galactic democracy, the Empire has been building a weapon (or weapons) or developing some sort of way of striking back against the Republic in an attempt to reclaim control over galactic politics. In the time leading up to TFA, the Empire has just struck a great blow against the New Republic and the time to re-ignite the conflict is at hand.
- I think the kids' story could go a few different ways: either Rey (and her brother) become orphans because Leia wants to protect them from political enemies / Sith sympathizers OR her children forge their own path: Rey is a pacifist and moves to the outer rim and her brother becomes a pilot for the Republic (following Han's footsteps).
- Leia's son falls victim to the dark side sometime before TFA. Having learned of his bloodline (knowing Anakin was once Vader), he believes he is the rightful heir to the Sith Empire. I believe the son is Kylo Ren or is influenced by him, and his motivation (in secret) during the film is to resurrect the SIth.
- The reason the Force Awakens and goes haywire is because multiple "Skywalkers" start using the Force. This is a problem because the Skywalkers come from an unnatural bloodline - they are literally children of the Force - and it throws the Force way out of whack. The dark side Skywalker (Ren) and the light side Skywalker (Rey) coupled with Luke's extreme power, send a ripple throughout the galaxy that awakens Force sensitivity in non-force users and exacerbates Force sensitivity in Force-users. The event turns the cold war into a hot war and sets in motion events of the ST: Finn does something Force-y in opposition to the Empire and gets hunted. He's introduced to Rey, who protects him and ultimately befriends him. They go to Luke, who is forced to re-enter the conflict. Rey embraces her destiny to become the last of the Jedi and confront her fallen brother.
- Ultimately, I think the only way the ST can end is if the Skywalker bloodline is destroyed. The Skywalker bloodline came from an unnatural place (the Force-birth) and the only way to restore balance is for Rey to sacrifice herself and kill her brother. Leia and Luke will die and I presume Han will too (because Harrison wants to go out in a blaze of glory).
That last part is really key for me: the only plot point that has never been addressed, but is ever-present and could be extremely key to the ST being relevant in any way is the matter of Anakin's unnatural birth. The Sith (Plagueis?), caused the Force to create a child and now that entire bloodline is responsible for throwing the entire galaxy out of balance. Therefore, the only way to fully restore balance is to end the Skywalker bloodline. This would give the Skywalker saga a clear beginning, middle and end.