I don´t know from where are the things that are chasing them, but 1 thing that i know is that that laboratory in the beginning sequence is a virtruska military lab that was working on transportation, communication and phase travel technology. (civilian labs are developing bio-hazzard matters) => We know that the vassari from the dawn of their space explration were finding strange structures positioned in gravity wells of planets where they arrived, and this devices even in a deactivated form were disrupting phase space trawelling. Even their brightest minds in thousands of years of technological revolution couldnt figure out how the devices were dirupting phase space, who build them and !why!, what other possibilities was the device capable of and mainly for a long time they even couldn´t copy the device. When the vassari developed nano technology they simply could build, clone the original devices atom by atom, molecule by molecule and they even figured how to activate its powers and it was simply named after what it was doing, the ...
PHASE INHIBITOR 
.
At least they were thinking they have fully activated it and its powers and positoned it over every their controled world to stop any revolt or to help defend it and it worked perfectly. Much of the vassari technology was based upon phase space maniplatin, their communitcation network wasnt an exception.
The Vassari swallowed up the bait - they were doomed - now the unknown enemy needed only that these curious fools activate the "extra" functions of even one device to allow them to enter normal 3D space from their home that is in the PHASE SPACE, isolated from that our own by the similar but naturally invissible energy field that is only visible when normal 3D space vessels travevel throw it and are engulfed by the field.
The Vassari scientist for thousnad of years were studying the PHASE INHIBITORS and "switching" off and on every button on them. And in the end they activated the right order of operation protocols that activated and ripped a chasm from our space to phase space throw which ships could travel to our space and "adapted" by the enrgy flux of the rift to physical and natural laws of our space (wasnt the need to engulfing the ships into phase field(a small bubble space) - the unknow PHASE SPACERS needed it like we when we were traveling throw their space => we all were untouchable from each other because of the interdimensional PHASE SHIFT energy-time-space difference).
The vassari were overruned by them in a matter of months. All vassari Phase travel engine, phase communication, phase space weaponry, logistics and supply was shutted down by the activation of the special abbilities of the now known PHASE SPACE MANIPULATOR AND PROJECTOR DIVICES .
The PHASE SPACERS fully activated remotely every device when they came to the next system to conquer, cripling comm, travel and weapons of the Vassarim then after a complete xenocide, they manulaly activated the RIFT OPENNING SEQUENCE and moved on.
And now the stupid TEC and ADVENT are stealing and installing by the vassari nano-atom-build, and dont reckognized yet as the cause of their fall and as a troyan trap, an unbelievable technology of the INHIBITORS into every system.
Ladies and gentleman, WE ARE SCREWED OOOOOOOOOOOOOOOOOOOOHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH NNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNNOOOOOOOOOOOOOOOOOOOOOOOOOOOOO !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
