Gigas somehow avoided most of the ill affects of the Cataclysm. To be sure, they lost much of their infrastructure, but their technology far outstrips our own. They are numerous too, they outnumber is greatly. In times past we might have stood against them but today? That becomes much more difficult.

As to their motives, I suspect they want our steel. From what little trade we have had with them we do know that our steelcraft is highly prized among them. I suspect they have long eyed our city's treasures, and now they feel strong enough to take it. Perhaps they shall, but they will find we were not idle these last 40 years.