What were the first borders between countries?

When air at the surface diverges, airflow above must diverge, regardless of hemisphere converge in the northern hemisphere but diverge in the southern diverge in the southern hemisphere but converge in the northern converge, regardless of hemisphere?

What benefits does this type of farming have?

Given: circle a externally tangent to circle b. how many possible common tangents to circles a and b can exist? 2 3 4