The technology that allowed people to
expand that much into the space is
"folding". It is a way to travel through another dimension,
nevertheless even this amazing technology has its limits and so the huge
ammount of energy needed on long-range travel is a great obstacle.
To adapt to fight with giant Zentradi, people had to come up with a new way to fight. New fighters were built that can transform into humanoid-shaped fighters. They were named Valkyrie.
These technologies were left behind by far ancestors of Zentradi, the Protoculture race.