In July, the European Central Bank announced the results of a thematic reverse stress test on geopolitical risk covering its 110 directly supervised banks. The design was elegant: rather than handing banks a scenario, the supervisor prescribed the outcome – namely, a depletion of Common Equity Tier 1 capital of 300 basis points – and asked each institution to work backwards to the geopolitical events that would produce it. The exercise confronted every bank with a deceptively simple question