As the seventh season of Game of Thrones drew to a close on Sunday night, a falling snow and a falling wall helped bring to fruition a promise fans have kept in mind from the show's very beginning: winter is coming. The change of seasons will surely affect the military plot of the episodes that remain for Season 8 — and as is typical for Thrones, the impact of the cold reflects a real concern from military history.
Everywhere there are seasons, from Ancient Rome to Civil War-era Missouri, those patterns have affected military history. Fighting when it's too hot, too cold, too wet or too dry can spell the end for an army. The effect of winter in the medieval period in much of Europe — the time from which much of the real-world inspiration for the fantasy series is drawn — is no exception.