why new technologies are making physical features less of a challenge when creating and changing national boundaries

Before things like mountains were typically boundaries since they were a pain in the butt to cross. But with modern planes, and depending on the mountian, cars, mountains aren't as big a pain anymore. Deserts might have also been a boundary before. Today you turn on the AC and drive straight across it. At least for technologically advanced western countries, there really isn't any geographic feature we can't easily get around.