Oh this reminds of a a cool concept I thought up one time when I was reading this website: http://www.futuretimeline.net/beyond.htm#250000000 Basically, in 250 million years, the continents reform back into one big super-continent, Pangaea Ultima. Also around this time, the sun increases in size and brightness, causing a lot of the water on Earth to evaporate, making it a very arid planet. So basically, in my concept, most of Pangaea is covered in uninhabitable deserts, meaning most of civilization exists on coastal cities. This makes interaction and trade between countries a very difficult and interesting concept. I imagine high speed trains would be one of the forms of travel across several thousand kilometers of desert. That and supersonic planes like the Concorde.