When Britain confirmed last September that it would recognize a Palestinian state, it was pulled in the wake of France, which had signaled a few months earlier that it planned to take the symbolically freighted step. On Tuesday, almost a year later, Britain was the one to seize the initiative. The British government announced, followed by France and Canada, that it would stop trading with Jewish settlements in the West Bank. It went so far as to accuse some settlers of engaging in the “ethnic cleansing” of Palestinians. This diplomatic sequencing speaks partly to domestic politics in each country. Last...