Borders cannot arise in a moment. A long trail of increasing opacity follows formal agreements and treaties: time is needed to break valuable connections and acquaintances among people and businesses, and to redevelop new ones according to recent economic factors and sometimes illegal activities like smuggling.
For a long time I observed the process of border arising between Ukraine and Moldova, former Soviet republics, down the Dniester river. Despite all formalities and penalties, illegal transportation was going on beyond big towns and check-points.
Yampil, a small Ukrainian town, attracted Moldova farmers from Cosăuți and Iorjniţa villages who crossed the river by oars and boats, especially on fair days.