In the comments I chimed in, giving an example to demonstrate the dangers of the standard discussion of GDP accounting. (Note that I’m not sure if anyone in the comments was saying something wrong; it was just a springboard for me to pontificate.) Let me embellish the example here:
Suppose Country A is composed of vegetarians whose sole occupation is to raise pigs. Each year they export all $1 trillion of them to their carnivorous neighbors in Country B. The meat-lovers, in contrast, do nothing but grow apples ($1 trillion per year) to sell to their vegetarian neighbors in Country A.
Further suppose that in each country, there is no investment (neither gross nor net). Each year, consumers in each country spend $1 trillion on food. There is no government.
So GDP = C + I + G + Nx = $1 trillion + $0 + $0 + ($1 trillion – $1 trillion) = $1 trillion.
That’s a tautology and obviously true. But when commenting on it, pundits might say something like, “Our country is driven 100% by consumption. Foreign trade contributes $0 to GDP, and thus has nothing to do with job creation.” Based on this misleading description, people might erroneously conclude that erecting a trade wall would do little to affect the economy.