-2404- By this time every human occupied planet, moon, and space vessel is under threat of being attacked by celestial forces. Humanity struggled to fight a war against an enemy not limited by distance or walls. On mars, the first genetically modified humans designed specifically for war are born: the orcs.
Orcs have unique physiology in that most of their organs have increased redundancy. Several organs could fail before an orc is mortally wounded. Their hormone balance is greatly altered, emphasizing strength and survivability. This was the race that would come to define mars.
-2418- 17 years into a losing war of extinction, Mars finally turns the tide with waves of orc warriors wielding weapons designed to kill celestials. In eight months celestial attacks on mars' surface gradually stopped. Earth was not so lucky.
-2420- Early indications, prophecies, and warnings told of humanity on earth being "wiped out". With the panic of a long war with entities that no one understands, most humans on earth fled across the solar system.
-2421- This is the year that earth fell. Exactly what happened on earth is debated to this day. whatever happened, it wiped out all humans still on earth, and any humans who enter earth's atmosphere inexplicably vanish in a burst of light, leaving their clothes and inorganic parts behind. After this event, celestial attacks suddenly stopped. Though there are confirmed intermittent reports of minor celestial attacks since then. This is considered to be the end of the celestial war, and most agree that humanity lost.
Experiments involving powerful beings of pure spiritual energy accidentally starts a large scale conflict with an unknown enemy that ignores every physical weapon and barrier.