The mood on the international conference call at the beginning of this month was somber as Ian Bremmer, president of the political risk consulting firm Eurasia Group, prepared to list off top global dangers in the coming year. Bremmer began with a show-stopping line: "If we had to pick one year for a big unexpected crisis — the geopolitical equivalent of the 2008 financial meltdown — it feels like 2018." The reasons are many, Bremmer cited, but the most prominent causes for global insecurity stem from U.S. President Donald Trump's move away from global leadership, and China's eagerness to fill...