Why Boarders?

Even at my age, I do not believe that I truly understand the reason for borders.  I guess being a free traders an believe that the exchange of goods and services services the world better that guns, bombs and bullets, boarders don't seem to make much sense.  At least they have a very limited purpose which the MSM just does not discuss or explore.  Our school systme is obviously incapable also.  Let's talk this though.