Civilizations that are failing build walls. Observe the great wall of china, and hadrians wall. Civilizations going to war build roads and railroads. Observe the economic expansionism of rome and the u.s. Civilizations that are acting defensively build military bases. Observe rome, spain, portugal, britain, and the u.s. Civilizations that are growing economically build airports and other non-military transport. The last two are contentious, the former because I haven't gathered enough counter examples, and the latter because I'm basing consumer airport spending on modern history, which by it's very (modern) nature, hasn't been around as a transport method very long. What can we extrapolate from these baselines, assuming they're correct? Russia isn't a threat. China is. UAE is going to have a real estate bubble. The U.S. has failed politically and is slowly failing economically (everyone knew this already). Anyone else want to give it a go? Edit: I'm in favor of The Wall, and this isn't a criticism of that, just an observation of a common symptom.