V is for VasariThe V ships look rather similar to Jarrasul Evacuators. And we've never gotten a good enough glimpse of the V's to discount them being Vasari.
V is for VendettaThe Vs have come to seek vengeance on humanity for what our long-forgotten Ancient Astronaut ancestors did to them when they were in a primitive state.
The Vs are ArtificialThe Vs were genetically engineered by Neglectful Precursors from Earth life. This explains how the V's biology is compatible with their human 'suits', how they can seemingly digest human food, and how Ryan can get his human girlfriend pregnant. Also, Anna mentions to Lisa that they where "designed" to be efficient, implying that they where created for a purpose rather than evolving naturally. They need Earth in particular, rather than the bazillions of other planets in the galaxy, because as their original homeworld it is uniquely suited to their physiology.
John May is Erica's ex-husband and Tyler's father.While he was apparently the leader of the 5th Column for a while, John May disappeared for some reason. Perhaps it was a similar situation to the one Ryan faced, where John fell in love with a human—Erica—and decided to leave the Resistance rather than put her in danger. They had a son, and somehow (admittedly, this is the biggest flaw in the theory) concealed Tyler's status as half-human, half-V from both him and Erica. Then, when he learned Anna and the V motherships were about to arrive, he decided that simply laying low wasn't enough to keep his family safe and decided to disappear completely. Unfortunately, Anna somehow became aware of John May's family, and that is why she's so interested in Tyler: because he's the only half-breed they know of, and because he could potentially help the Vs to find John May.
Tyler is a half-human, half-visitor hybrid.This is the big secret about him, and Erica and Joe have always known about it. In addition to this, Joe must also either be a V or he isn't actually Tyler's real father (going on the theory above that John May is). It's hard to tell if Anna knows of this or not, but given how special he seems to be to Lisa's 'destiny', it seems probable. It's also possible that Erica may not be his real mother either.
Erica is part or full V, and Valerie will also become one.Going by what Joshua said to Ryan that there'd be 'no going back' once he gives Valerie the phosphorus, and that a human cannot survive the pregnancy, this seems to be the likely outcome. If Tyler is in fact a hybrid, then the same thing must have been done to Erica as well (if she is his mother), and she has always known about it.
Anna is an Eldritch Abomination, and not really a V.Except for (maybe) her daughter, she truly doesn't care about anything or anyone but herself and is using both the Vs and humanity for some truly evil purpose. At some point in the past, she took the form of a V (and killed the real Anna, if there was one) and enslaved the entire race. Her ultimate goal is either to rule / destroy the universe (of course), or release some horrible Sealed Evil in a Can that is her master and much, much worse than her.
The Visitors are actually from Earth in the first place.This is even foreshadowed in the second part of the first miniseries when a scientist talks about how the dinosaurs would have evolved into intelligent tool users. The Visitors evolved then, saw the asteroid coming and managed to escape the planet. They went to Sirius in a trip that took millions of years via Generation Ships. By the time they got there, they only had a few thousand years to develop faster-than-light drives. Eventually they wore their new home planet out of resources and turned their eyes back towards their own home. This also explains why the visitors can eat Earth lifeforms.
The series is a prequel to Starship TroopersOh, the resistance was all about democracy, but them silly humans never learn. With the visitors gone (ignoring the TV series), Earth went totalitarian and paranoid in setting itself up to be defended from any and all outside threats. Radchack is obviously Ham's Identical Grandson.