The Cheviot Hills and the River Tweed.
Hadrian's Wall may not be as natural but it is 75 miles long and built by the Romans. It borders England and Scotland.
The Cheviot Hills.
mountains
the 2 boundaries of England are Scotland ad wales
The Natural Barriers in canada are Molten lava and cars
Oceans are some of the natural barriers in the planet.
The natural barriers and isolation allowed China to
no natural barriers are rivers, cliffs...... natural stuff not man made
Mountains and oceans are the natural barriers of western africa
Batman
unpredictable flooding of natural barriers for protection . Natural Resources limited.
monsoons
The body has a number of natural barriers, your skin, your eyelashes, mucus and even tears are all natural barriers to name but a few.
Most of the borders of the U.S. are marked by oceans; the next most frequent natural barriers are rivers.