If Britain plunders a quadrillion worth of stuff and ships it home, their GDP does not have to change at all. It's just not what GDP measures. The only way GDP

If Britain plunders a quadrillion worth of stuff and ships it home, their GDP does not have to change at all. It's just not what GDP measures. The only way GDP is can be useful if we say that by wealth we mean GDP, but then we've just made the word wealth as useless as the GDP metric. In the case of countries, our modern intuitive understanding of wealth is pretty much "how hard does a person in this country have to work in relation to how well they live" - at least that's what countries nowadays are optimizing for. A country in which <40 hour work-weeks are the norm, in which almost everyone can afford yearly week-long vacations, which has good infrastructure, as well as affordable high-quality services, food and goods, you'd probably call rich. That's just not something GDP tells you in a vacuum. Often when looking back at the time of empires, our understanding of wealth becomes "how much actual wealth have the rulers of this country managed to accumulate", which is also not something GDP measures very well.