The rulers of Tiamat were very greedy, controlling and aggressive — as previously mentioned. They viewed the inhabitants of Mars with envy and greed.
Although they did not previously dare attack Mars openly (the very advanced Builder Race lived on the planet and protected it), the acquisition of their death star gave them a sense of invincibility, and they declared war on Mars.
Two hydrogen bombs were exploded in the northern hemisphere of Mars, killing millions. Only a small number who had taken their rulers to underground bunkers, survived.
Why were the rulers of Tiamat envious of the Martians?
The Martians were their distant genetic 'cousins'; they had the same genetic origins. The overuse of technology had destroyed the people of Tiamat's connection with the environment and their natural environments were dying. Whereas the Martians were technologically brilliant (taught by the Builder Race who lived among them) and they had forged strong allies, such as some races in Orion.
To be continued...