… is from pages 212-213 of Deirdre McCloskey’s pioneering and persuasive 2010 volume, Bourgeois Dignity  (original emphasis):
If borders were such an engine of growth, the economist points out, then one could draw an international border in England from Dover to Wroxeter, calling “foreign” all trade across the Watling Street border thus created, into and out of the ancient Danelaw, and thereby make trade within England into an engine of growth. Or you could call left-handed English people “foreigners,” and achieve the same result. The accounting reductio shows that there cannot be something special about foreign trade.
Yes. Yes. Yes to the billionth power and for the trillionth time.
Your sales of goods or services to people who reside in different political jurisdictions than the one that you reside in do not generate for you and your neighbors some special type, or extra quantum, of wealth that is attributable to the fact that your customers are ruled by a sovereign different than the one that exercises authority over you. And your purchases of goods and services from people who are ruled by a sovereign different than the one that exercises authority over you do not produce for you and your neighbors any economic consequences that are unique to your choosing to patronize those differently-sovereigned sellers.