For world-builders who work upwards, from physical detail to people, there comes a phase in every project when you have to worry about climate: the long-term patterns in weather that will matter to the civilizations of your world. This article is a practical guide to getting yourself a decent, believable climate without enormous amounts of work. You can consider this a first-order approximation of climate; there are many ways to add more detail and realism, and I’ll point some of these out as we go. I often do world-building with the computer, but here I’ll mostly talk about drawing on a paper map, for simplicity.
In my previous article on the geometry of empires, I considered two essential strategies for organizing the defense of a territory. In one, troops were positioned along the border, ready to intercept enemies but spread thin. In the other, a single, centrally-located force was powerful but slow to respond. These are extreme approaches, though, lying at the ends of a spectrum filled with intermediate strategies.
The pre-modern state aims to defend its borders against enemies. The size of its territory, though, has profound implications for how it can do this; which may in turn influence how that state develops--whether, in particular, it seeks aggressive expansion.