Countries borrow in dollars because dollar debt markets are deep and liquid. This paper develops a theory of when that dominance becomes fragile because countries have inherited dollar liabilities but increasingly earn yuan-linked revenues. In the model, countries begin with dollar-denominated sovereign debt. Geopolitical fragmentation raises their yuan revenue share through two channels: higher trade barriers with dollar-linked markets shift exports toward yuan-linked markets, and higher costs of using dollars in that trade make yuan settlement more attractive. Governments then face a choice: repay dollar debt using revenues that are less dollar-linked, default, or restructure into yuan. [...]