"Sell a country! Why not sell the air, the great sea, as well as the earth? Did not the Great Spirit make them all for the use of his children?" – Tecumseh, Shawnee leader
This idea means that a nation cannot be sold. Tecumseh believes that "a country" is for everyone to use; it is not a commodity.
He compares a country to the air and the sea -- these things cannot be sold; they are too great to sell. They are for everyone. He says a country is the same -- it is universal, not sellable.