Why are the capitals of central Asian countries right against the borders?
Dushanbe, Tajikistan; Ashgabat, Turkmenistan; Bishkek, Kyrgyzstan, and Almaty, Kazakhstan are capital cities that are nestled up tight against borders, with tremendously large countries stretching away from them. Indeed, these capitals are quite close to each other, in relation to how large each one's countries are.
Why is this? There is no rule that Central Asian capitals must be like this. Compare Tehran, Kabul, and Tblisi that are relatively more central.
Of course, each one has its own history, but is there something in common to those four border-capitals?