When you talk to the analysts and policymakers who worry about the possibility of war between the US and Russia, the scenario you most often hear begins in the tiny Baltic nation of Estonia, along Russia's border. Estonia is today part of NATO, which obligates the US and most of Europe to defend it from attack, and the US is deploying heavy military equipment there to deter possible Russian aggression. Estonia, formerly part of the Soviet Union, still has a large Russian minority that is served by Russian state media and has participated in incidents of unrest in the past.

The fear is that Russia could attempt to exploit or stir up unrest among Estonia's Russian minority, as it did in 2014 in eastern Ukraine. If such a crisis escalated, NATO's member-states could split over whether to respond — effectively dissolving NATO, as may be Vladimir Putin's hope — or, all too easily, the violence could escalate out of control into war, even nuclear war.

This flowchart, designed by Javier Zarracina, illustrates the decisions that US and Russians might make in a crisis, and where those decisions would take us. Many of the threads, as you can see, end in peaceful resolution, or something short of all-out war. But many do not, and at a certain point the logic of escalation become more difficult to resist: