The document discusses the balance of payments identity and how it accounts for changes in a country's external wealth over time. It makes three key points:
1. A country's external wealth is equal to the value of assets it owns abroad minus the value of foreign-owned assets in the country. It can increase through current account surpluses, capital account surpluses, or capital gains on assets.
2. Changes in a country's external wealth come from financial flows that increase or decrease external assets/liabilities, and valuation effects from changes in asset prices.
3. For the US, valuation effects from capital gains have significantly reduced its external debt over the past 30 years compared to what financial flows alone