See also no man's land
In World War I,the land between the enemy lines, the land between the trenches that delineated the disputed borders between nation-states arguing over turf, was called no-man's land. Not only did it not definitively belong to either side, it was suicidal for any man to go there.
When a border between states has two walls, for instance the Berlin wall, which "Consisted of two walls, 50m apart from each other, between them an area with mines etc." the buffer zone between the walls is a no-man's land.
No-man's land is:
Land that is not under the control of any state
Territory that is not safe to enter.
A border area that is hotly disputed.
A zone where competing spheres of influence meet and cancel each other out.
A place where no authority reigns.