Fortified frontiers

Name(s): 
Frontier barriers
Fenced frontiers
Nature 
Ditches, barbed wire fences, brick and stone walls are all means of building obstacles between two peoples, sometimes to keep one group in and sometimes to keep the other group out. The Great Wall of China, the Maginot Line, and the Berlin Wall are examples.
Incidence 
The USA is currently digging a ditch 1.5 metres deep and 4 metres wide near the main border crossing with Mexico at Tijuana to "address a security and safety concern".
Broader 
Divided countries
Intra-continental divisions
Disturbance to wildlife patterns of movement
Reduces 
Loss of internal political borders
Aggravates 
Divided geographic allegiance
Aggravated by 
Social divisions
Violence along internal borders
Reduced by 
Illegal movement across frontiers
Strategy(ies) 
Reuniting countries
Managing divided cities
Fortifying frontier lines
Establishing frontier barriers
Value(s) 
Barrier
Type 
(D) Detailed problems