U3 Ideas:
This is my idea/clues for the 3rd Movie. SPOILERS MAY BE IN THIS THREAD.
First and foremost, while understandably the war between vampires and lycans is enough for all of us to shake a stick at, I think there is a couple of clues within the movie that people are eluding to the final installment of the series. Humans. Kahn then finds bullets that are "government engineered"(by the way Tenius was the supplier to Lucian, not the creator of the bullets as he said).
One thing I always find interesting is the "RULE" set by Victor to not harm humans. It was said by Selene when speaking to Kraven, about "the lycans attacking us in public". Later on, Kraven in sneering fashion says "never could obey his own rules". Next Selene in the second movie says to Michael "you don't want to kill a human, you wouldn't want that on your conscience". Then as the Vampire agents of Arctavius tries to destroy a Vampire testing lab, they do not kill the humans, they simply immobilize them. Same with Selene when the police was attacking Michael. Finally, if you look through the entire movie, you do not notice any humans ever being killed. Except in the ancient days of Medieval times, of the village being destroyed(even though I'm not sure if they were human in the first place), and Selene's family destroyed.
Why? It is very simple, humans are the ultimate mastermind and controller of all Vampires and Lycans. They agreed to allow them to live and fight their meaningless war in the modern era, so as long as no humans are harmed.
My theory is that humans long ago made a stand against the evil which Vampires and Lycans represented. In that way the Lycans and Vampires were to remain dormant and keep their war within their territory that perhaps the humans gave them. Which is precisely why humans were the creator of William's cage, and Vampires were told to control the Lycans or else it meant the death of all of them. This being the reasons despite Vampires being so powerful, can not ever fight anything but small underground war.
My theory for the 3rd movie: Underworld: Annilhalation(narrative by Kate Beckinsale). The war between the Lycans and Vampires has always been one of secrecy. For thousands of years we fought, never arousing the attention of humanity. I was once a deathdealer in this battle. I believed in our mission, until the truth of my beloved step-father Victor was revealed, whom I killed. While attempting to unlock the truth of our past, I fell in love with Michael. The forerunner of Alexander Arctavius, the first immortal and the father of both the Vampires and Lycans. As the truth was revealed, I learned that Arctavius was still alive, and the horrible truth of Marcus the first true vampire, and William the first lycan was actually his sons. Unknowingly to me Marcus was awoken with knowledge of what had transpired, and began his mad quest to release his brother from the prison which Victor had built, and hidden. In the aftermath, Arctavius killed his father and gained the key to at last open William's jail. In the last deed of his long life, Arctavius granted me his power, and in turn I became the only carrier of the original blood of the immortals. To stop Marcus, Michael and I met him and his brother William in mortal combat. We won. The lines which once divided Lycans and Vampires are blurred, as we now learn of our common heritage. The old hatred which once ignited our fears and anger, is now replaced by confusion and uncertainty. The future is uncertain now, yet I fear the war is not yet over, but only begun.
This is where I come in. In light of the recent subway battle, forest fighting, and shipyard explosion. The battle between Lycans and Vampires has poured on to the streets of humanity. The human world who has watched idly by will now be force to become involved in a war which they had not been for thousands of years. The lessons of useless mercy once displayed by their predecessors will be thrown out. The ultimate goal now: Destruction of all Lycans and Vampires at all cost to save humanity. The Lycans and Vampires now must band together for the first time ever to ensure their future.