H.D. Miller says better than I would have something I've been meaning to write about the last couple of days:

This period of felicitous climate in the Central Middle Ages has long been known as The Little Optimum; called "optimum" because the warmer climate enabled a flourishing of agriculture in Northern Europe. England, which during the Little Optimum enjoyed the climate of Central France, even developed a substantial wine industry, an industry which was frozen out of existence at the start of the Little Ice Age. It was also during this period that Viking explorers gave Greenland its improbable name and found grape vines growing as far north as present-day Newfoundland.

Full caveat: I'm no Medievalist, but as part of one of my hobbies, and as part of my course of study in undergrad, a good grasp of English and Western Continental (and indeed, Continental) history from about 900 A.D. to about 1500 A.D. was vital. So I'd forgotten the term "Little Optimum," but I did know this:

Military conquests are both easier and less likely in warmer temperatures. If it's warmer, it's easier to move around; swing armies over sea and land; keep your troops supplied; fight longer days, during longer periods of the year, than otherwise; and keep your troops from dying of illness and starvation in general. It's also possible to build up food reserves, so that you don't need to be as worried about leaving during harvest time.

But, because harvests are more bountiful, and winters less harsh, two of the biggest causes of conflict become less. War happens less frequently, as one professor of mine liked to put it, because there's less to fight over, and more to get drunk and get laid over. (His words, not mine.) Populations grow. Political systems mellow, because resources are less scarce.

Put it this way: Aside from the spate of millennial violence right after 1,000, Europe was a pretty calm place, all things considered, during that Little Optimum. Then check out what happened at the end -- the Great Schism (or the Second Great Schism, I lose track), the meaningless Crusades, the Welsh revolt, the Hundred Years' War, the Scot revolt, the purging of the Knights Templar, famine, plague, Catharists, Spiritualists, Albigensians, burned Jewish ghettoes, and so on, and so on.

H.D., of course, could and did make this point better. But it's late, and I'm rambling.