#Isolationism

Why does trading with more people matter?

I can understand the importance of technology, more people, means a scientific problem is solved sooner, thus there is value in trading technology, that oneself is not left in stone age.

I understand that some groups due to environment, secrecy, copyright, or choice,

Have monopolies,

Crops grow better in some regions, only Greeks know how to make the Fire, Coke is owned by a company, Detroit makes the cars.

But once you have a location, within your own territory, or a partner, what does it matter if someone refuses to trade?

Take the American Confederacy, Britain, and India,

As I recall, the Confederacy tried to use fact that Britain traded for their cotton as diplomatic leverage, but Britain simply shifted to using India more for cotton.

The Greeks had the secret of Greek Fire, 'but technology is possible to be discovered by others.

Modern Flamethrowers, Roman Concrete forgotten then reinvented, so on.

Coke has copyright on Coke,

But WWII Germany can just invent their own soft drink, Fanta. One also see's countries ignore copyright, and create their own knockoffs of culture, China and it's banning of certain Western media, and conveniently inventing their own similar.

Detroit made the cars, until they didn't, we all know what happened to Detroit.

. . .

I also understand what investments 'can be made in other countries, and it hurts when these investments are 'suddenly taken away or illegally confiscated.

But surely not all one's 'necessities are invested in other countries?