There was a terraforming plan but it failed and the technology was released uncontrollably
According to the historical background on the main site
, the Votans expected Earth to be devoid of intelligent life, so they thought they'd be terraforming a world that was free for the taking. Once they found out there were already inhabitants, they put their terraforming plans on hold as they negotiated with Earth's governments for settlement rights, and then they only planned to terraform the regions of the planet that they'd been granted as enclaves (though there was certainly controversy about it on both sides). The Pale Wars intervened and no deliberate terraforming efforts were ever made. But in 2030, some unknown event caused the Arks to explode and the Terra-spires to be released, causing an out-of-control global terraforming event that killed huge numbers of both humans and Votans.
It seems like there's some unknown player that's an enemy of both the humans and the Votan immigrants -- that's responsible both for smuggling the Volge aboard the Ark fleet and for destroying the Arks.