When? Not for a long time. Slavery and witchcraft were historically very popular ...
> when you buy stuff you're losing wealth
That's a incredible failure of understanding. I can't believe that's the basis of mercantilism. Why would anyone buy something?
If you buy a house for $100,000, your wealth remains the same - you replace $100,000 in cash with a $100,000 house (ignoring complexities like a mortgage, transaction costs, etc.). That is basic accounting, of course.
In fact, your wealth probably increases: The house's value is <$100,000 to the seller and >$100,000 to the buyer, or else they would be disinclined to make the effort of making the deal - it would be like trading a $10 bill for a $10 bill, with lots of time and transaction costs. Market value - the value to others - may remain the same or vary, of course.
The economy works because people make these value-increasing transactions. I take $10 of inputs, manufacture $20 worth of output, and sell it to you for $15. We both gain $5. If your business isn't producing more output than its input, you're going to be out of business soon.
Many transactions are better with people who happen to be outside the borders of your country - why wouldn't they be?