Witnesses like to apply it to ecological ruin, as if the Bible was predicting the environmental crisis we are currently in. However, the marginal reference in the NWT to Rev. 11:18 is to Gen. 6:11: 1 But the earth had become ruined in the sight of the true God, and the earth was filled with violence.
So "ruined" refers to being ruined by violence, which aligns with the idea of "corrupt" or "corruption" as already mentioned and not with ecological ruination. The JW misinterpretation of Rev. 11:18 was one of the final straws that broke my publisher's back. The last time I was out in field service, I read that scripture at the door and recited the orthodoxy about how the Bible was predicting the ecological ruination we see around us, even though I knew that was an eisegetical error. My conscience killed me afterward and I thought to myself--never again.