Last week offered fresh evidence that the most consequential historical shift of the last 100 years continues: the decline of Europe as a force in world affairs. As Deutsche Bank warned of a German recession, the European Commission cut the 2019 eurozone growth forecast from an already anemic 1.9% to 1.3%. Economic output in the eurozone was lower in 2017 than it was in 2009; over that same period, gross domestic product grew 139% in China, 96% in India, and 34% in the U.S., according to the World Bank.

As its economy lags...