Gods, people have been discussing that as long as we have records. Anywhere from their life energy being necessary to change (or save) the world to they wouldn't if the bloodbaths and battles didn't happen. Ninety years is long enough you're not likely to see more than one cycle if you see one at all. Hard to get definitive on that timescale.
First year's usually pretty good. The second one things go nasty.
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First year's usually pretty good. The second one things go nasty.