The diplomatic dance of managing allies can mimic that of a romance, complete with courtships and jealousies. Rivals such as China and Taiwan often put other nations in the awkward but flattering position of being a coveted prize, wooing them with contracts, foreign aid, and political promises. But what happens when the object of their affection undergoes a sudden change of heart?

Yu-Shan Wu, a political scientist at National Taiwan University, raises this question in the March edition of Issues & Studies, a quarterly publication of the Institute of International Relations in Taipei. In his forward-looking essay, “From Romantic Triangle to Marriage? Washington-Beijing-Taipei Relations in Historical Comparison,” Wu argues that American regime change has turned the triangle into a marriage between the United States and Taiwan while transforming the People’s Republic of China into a pariah.

Wu notes the recurrence of such arrangements throughout history and chooses the 19th century triangulation between Berlin, St. Petersburg, and Vienna as the best metaphor for today’s trans-Pacific relationship. In that scenario, a newly united Germany was aggressively courted by both Russia and Austria-Hungary. German Chancellor Otto von Bismarck attempted to create a ménage à trois, all the better to isolate France. But the threesome quickly split: Russia and Austria-Hungary bickered over the Balkans, leaving Berlin to vacillate between two enemies. A new, idealistic kaiser eventually fell out with Bismarck and declared Germany’s devotion to Austria-Hungary in 1890.

This drama, Wu believes, is again unfolding between Washington, Beijing, and Taipei. The cast does seem to bear a remarkable resemblance: A nascent...