How is a border divided?

With a consensus among neighbors. In general, geographical features mark the  boundary  that appears on maps. The reason  is  practical: mountains, rivers, lakes  and  sea ​​arms serve to divide territories more safely  and  make it difficult to invade. Linear currencies, such  as  those in the United States, Canada,  and  much of Africa, are exceptions established for political and  bureaucratic reasons  . Throughout history, no currency has proved definitive. All of them, at some point, have changed, Because until the 20th century the borders between countries and  states were largely ignored - invading a territory rarely caused  a  crisis. Today this binge  is  more contained, as there are international bodies, such  as  the UN  and  the Hague Tribunal, to solve impasses  and  contain exalted spirits.

Rivers
define a considerable part of the borders. In war, they have a great strategic advantage, since the one that decides to cross a river of currency ends up exposing itself too much  

Examples - The Danube, in Europe, draws borders between ten different countries. The territory of The Gambia is limited to the banks of the homonymous river

Cordillera Mountains form an excellent defense barrier and help set boundaries with ease    

Examples - The Dângrêk mountains are disputed between Cambodia and Thailand. The Cordillera del Condor has already provoked an armed conflict between Peru and Ecuador   

The world's largest lakes separate several countries simultaneously. Disputes occur in navigation and commercial exploitation  

Examples - Khanka marks the currency between China and Russia. And Lake Victoria separates Uganda, Tanzania and Kenya      

•  The CIA estimates that there are now 189 regions with territorial disputes
• They form obvious divisions between countries. But peninsulas andcontinuous beach arms may pose diplomatic problems  
  Examples - The Strait of Gibraltar has been disputed for centuries by the United Kingdom (which controls a territory in the region) and Spain. Chile and Peru do not understand each other's maritime boundaries. On the high seas, the Spratly Islands are a tug-of-war between China, Taiwan, the Philippines, Vietnam, Malaysia and  Brunei