Here's my theory. It's totally derived from bits and pieces of backstory posted from time to time by Frogboy and from the new TA race descriptions and tech descriptions.
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In 2228(TA), the Terrans somehow break out from the impenetrable barrier around Earth. Apparently, a Terran ship meets an Arnorian, who possibly helps them break out from the barrier, and tells them how the Dread Lords got their power. The DLs power, according to said Arnorian, is from their life-force crystals(as well as inherent Precursor abilities). They had created life-force crystals by somehow, using an unknown 'device', stealing life-force from the Arnorians and helping to trigger the Precursor mega-war we all know of. My hypothesis is that this 'device' is the 6.2 billion-year-old Spore that the Korath have discovered, which crystallizes protein. The Korath, however, have no clue how to use these crystals. Since the Dread Lords are also controlling the Korath, the DLs may also be benefiting from the crystals created in Korathian spore attacks. The Terrans are given a mission by the Arnorian: Find all those DL crystals and destroy them in a supernova. And since supernovae don't come by often, the Terrans must artificially cause one by using Terror Stars. Thus, you have the Twilight of the Arnor campaign. The Dreads are probably destroyed in this, but I'm not sure since no one has actually played the TA campaign yet.
Flash back to 2225, when the Terran navy, having beaten back the Dread Lords, is banished into the pocket universe. This is also when the Thalans arrive, supposedly too early. 5 years later, in 2230, the Terran navy returns from the pocket universe with 'stuff' - possibly shards of the Telenanth or other goofy Mithrilar objects, and this 'stuff' destroys or triggers the destruction of the universe.
However, one person doesn't return from the pocket universe. This is D.L Bradley, aka. Draginol. He somehow obtains supernatural powers and becomes the 5th Mithrilar, i.e, the Dark Mithrilar. He is in fact, more powerful than the 4 original Mithrilar, which is bizarre. He creates 1000 beings similar to himself, which have all the properties of humans like himself, but vastly more powerful individually. These are the Dread Lords, who, like us, can sense time. Then he created 10000 beings just like the Dread Lords, but with lesser powers. These are the Dread Knights, who are minions to the DLs. Then he created beings similar to humans, but lacking the ability to sense time, yet still far more powerful than individual humans. These are the Arnor. Draginol also somehow causes the 'shattering of the Telenanth', which alters the laws of physics and enables other life life forms to evolve naturally. He eventually goes to the planet Altaria, which is where he dies, but not before triggering the sudden evolution of the Altarians, who are also very similar to humans but have very, very slight supernatural powers, to the point that they're negligible and near-invisible.
In this pocket universe, other sentient life evolves. The Precursors have their mega-war and vanish again. All the races from the 'real universe'(the one which possibly gets destroyed in 2230) also evolve in this parallel universe. My hypothesis here is that the Thalans also evolve in this universe. The Thalans live to the point of time that the altered laws of physics, which allow for life, are no longer sustainable, thus causing them to realize that the pocket universe is 'dying' again and everything will be reduced to subatomic particles. Due to some freak connection which I can't imagine, the Thalans develop trans-dimensional time-traveling technology and somehow travel to the real universe in Earth year 2225 - which for some reason, is 5 years too early.
Whether they can save the universe from the Terrans' hapless but catastrophic mistake is unknown. That is stuff for GalCiv 3.
