Earth side history
Earth year 2013 a race of giant humanlike aliens invaded the earth killing millions of humans in the process. The humans lucky enough to avoid being killed were rounded up into Sanctuaries built by the aliens to keep the human species alive but kept them from advancing more in science and technology so that they wouldn't get any ideas that give them the idea to oppose their giant masters.
Titan side history
The Titan year 30000 the titans have conquered a vast amount of planets. Their final planet they needed to conquer is the planet earth. When they landed on the planet their ships landed ontop of each capital city destroying them and killing all inhabitants. They then proceeded in capturing humans and destroying all human made buildings in preparations to build their own cities. In the overall process they captured a third of the human population and killed the rest. The first buildings they made they called Human Sanctuaries which is owned and ran by one of the titans 12 generals.