As politics around the world pull apart, can the center rally?

Amid the polarization of the world today, some are increasingly calling for a return to the moderate middle. But centrism’s definition, popularity, and practicality all depend on where you are standing.

Around the world, politics are polarizing and leaders are ruling from the further reaches of the political spectrum. In today’s belligerent global mood, is there any fruitful ground for a moderate politician to plow?

Starbucks founder Howard Schultz thinks so; he says the U.S. two-party system is broken, and he’s planning an independent bid for the presidency. In London,...