When questioned about prosecuting the 2003 war in Iraq, then Major General David Petraeus famously asked, “Tell me how this ends?” That question is even more relevant today regarding Ukraine. Recall Iraq disintegrated into a widespread insurgency in 2004 that General Petraeus would have to suppress two years later. During that war, then defence secretary, Donald Rumsfeld, had coined the notions of “known, knowns; known unknowns; and unknown unknowns.” The last two categories apply to Ukraine. In terms of postulating what might come next in Ukraine over the coming days, weeks and even months, the unknowns are daunting. Start with the known unknowns. What might be Vladimir Putin’s more extreme options in waging this brutal and obscene war against civilians? First, Putin might expand Hitler’s terror tactics of the Blitz and the bombing of London by increasing the atrocities Russia is committing in Ukraine. Second, would a desperate Putin employ a nuclear weapon possibly threatening to destroy Kyiv if Ukraine does not surrender or in anger or as a demonstration? Or would he use chemical weapons as Bashar al Assad did in Syria? How would the civilized world react? Would the US consider retaliation as it did against Syria’s use of chemical weapons or are the risks of escalation too high? In any event, these scenarios must be considered along with a range of responses. Putin might expand Hitler’s terror tactics of the Blitz and the bombing of London by increasing the atrocities Russia is committing in Ukraine. Third, suppose Ukraine’s courageous President Volodymyr Zelensky is assassinated? Is there a succession plan in place? Or would decapitation of the leadership end the war? What would we and NATO do? Fourth, suppose Putin controls Ukraine east of the Dnieper River. Would the country be partitioned much as Korea and Germany were after World War II and would that end hostilities or would that spark an ongoing conflict or simmering grey zone war? The unknown unknowns are the most dangerous and threatening because of their unpredictability and hugely destabilizing potential. Putin could declare that any state providing weaponry to Ukraine is belligerent and thus can be targeted. Poland, Romania and Hungary, Ukraine’s border states, could suffer punitive cyber attacks and even missile strikes to seal off roads and land transport routes that could kill or wound citizens of those countries. Would that constitute grounds for invoking NATO’s Article 5? Putin could fortify Kaliningrad, its tiny enclave in the Baltic separated from Russia by Poland and Lithuania. Putin could send more troops to Belarus, deploying them on the western borders as a direct threat to NATO. Russia could also deploy the Baltic Fleet as a further warning. Concurrently, what covert actions might the US, NATO and others be undertaking to disrupt the Russians? Resupplying Ukraine with anti-air, armour and personnel weapons; logistics from body armour to food, batteries, communications, surveillance and other vital items; to, possibly, fighter aircraft and surface to surface missiles is top of the agenda. However, what cyberattacks, influence and information operations to affect Russian forces and the Russian public may be underway is an unknown unknown. Further, contingency planning must be underway for several worse or worst-case scenarios: NATO in the event of Russian escalation against it and its members and Ukraine if the government falls whether or not one in exile or Lviv is established. The time frame is both immediate and the long term should Ukraine descend into an insurgency. And what can be done to influence Russian elites and citizens to protest the outrageous and unconscionable invasion of Ukraine and the reign of terror waged against its citizens? Unlike the aftermath of the sneak attacks that brought America into World War II and the Korean War, the strategic aims then were straightforward. Wage a war of unconditional surrender against Japan, Nazi Germany and Fascist Italy and repel the North Koreans from the south. Ukraine is far more complicated. For example, banning Russian oil and gas sales to Europe would cripple those states and hence is unacceptable, so far. And while the US is attempting to renegotiate the Joint Comprehensive Plan of Action (JCPOA), Russia is a signatory and its assistance may be needed. The conclusion of this cursory examination of how this conflict ends in Ukraine is incomplete. What is needed is a thorough examination of this range of knowns and unknowns to develop a broad set of options that cover these and other contingencies. The purpose is to ensure that future surprise is minimized and that steps can be put in place now to avoid or mitigate what could be a disastrous worst case. The writer is a senior advisor at Washington, DC’s Atlantic Council and a published author