When Russian President Vladimir Putin ordered his invasion ^[1] of Ukraine on 24 February, he envisaged a quick seizure of Kyiv and a change of government analogous to Soviet interventions in Budapest in 1956 ^[2] and Prague in 1968 ^[3]. But it wasn’t to be. The war is still raging, and no one knows when or how it will end.

While some observers have urged an early ceasefire ^[4], others have emphasised the importance of punishing ^[5] Russian aggression. Ultimately, though, the outcome will be determined by facts on the ground. Since it’s too early to guess even when the war will end, some conclusions are obviously premature. For example, arguments ^[6] that the era of tank warfare is over have been refuted ^[7] as the battle has moved ^[8] from Kyiv’s northern suburbs to the eastern plains of the Donbas.

But even at this early stage, there are at least eight lessons—some old, some new—that the world is learning (or relearning) from the war in Ukraine.

First, nuclear deterrence ^[9] works, but it depends on relative stakes more than on capabilities. The West has been deterred, but only up to a point. Putin’s threats ^[10] have prevented Western governments from sending troops ^[11] (though not equipment) to Ukraine. This outcome doesn’t reflect any superior Russian nuclear capability; rather, it reflects the gap between Putin’s definition of Ukraine as a vital national interest and the West’s definition of Ukraine as an important but less vital interest.

Second, economic interdependence doesn’t prevent war. While this lesson used to be widely recognised—particularly after World War I broke out among the world’s leading trade partners—it was ignored by German policymakers such as former Chancellor Gerhard Schroder. His government increased Germany’s imports of, and dependence on, Russian oil and gas ^[12], perhaps hoping that breaking trade ties would be too costly for either side. But while economic interdependence can raise the costs of war, it clearly doesn’t prevent it.

Third, uneven economic interdependence can be weaponised by the less dependent party, but when the stakes are symmetrical, there’s little power in interdependence. Russia depends on revenue ^[13] from its energy exports to finance its war, but Europe is too dependent ^[14] on Russian energy to cut it off completely. The energy interdependence is roughly symmetrical. (On the other hand, in the world of finance, Russia is more vulnerable to Western sanctions ^[15], which may hurt more over time.)

Fourth, while sanctions can raise the costs for aggressors, they don’t determine outcomes in the short term. CIA director William Burns ^[16] (a former US ambassador to Russia) reportedly met with Putin ^[17] last November and warned, to no avail, that an invasion would trigger sanctions. Putin may have doubted that the West could maintain unity on sanctions. (On the other hand, Chinese President Xi Jinping has offered only limited support ^[18] to Putin despite having proclaimed a ‘no limits ^[19]’ friendship with Russia, perhaps owing to his concerns about China becoming entangled in US secondary sanctions.)

Fifth, information warfare makes a difference. As RAND’s John Arquilla pointed out ^[20] two decades ago, the outcomes of modern warfare depend not only on whose army wins, but also on ‘whose story wins’. America’s careful disclosure of intelligence about Russia’s military plans proved quite effective in ‘pre-debunking’ Putin’s narratives in Europe, and it contributed greatly to Western solidarity when the invasion occurred as predicted.

Sixth, both hard and soft power matter. While coercion trumps persuasion in the near term, soft power can make a difference over time. Smart power ^[21] is the ability to combine hard and soft power so that they reinforce rather than contradict each other. Putin failed to do that. Russia’s brutality in Ukraine created such revulsion that Germany decided finally to suspend ^[22] the Nord Stream 2 gas pipeline—an outcome that US pressure over several years had failed to achieve. By contrast, Ukrainian President Volodymyr Zelensky, a former actor, used his professionally honed dramatic skills to present an attractive portrait of his country ^[23], securing not just sympathy but also the military equipment that is essential to hard power.

Seventh, cyber capability isn’t a silver bullet. Russia had used cyber weapons to intervene in Ukraine’s power grid ^[24] since at least 2015, and many analysts predicted ^[25] a cyber blitz against the country’s infrastructure and government at the start of the invasion. Yet while there have reportedly been many cyberattacks during the war, none has determined broader outcomes. When the Viasat satellite network was hacked ^[26], Zelensky continued to communicate with world audiences through the many small satellites provided ^[27] by Starlink.

Moreover, with training and experience, Ukrainian cyber defences have improved. Once the war had begun, kinetic weapons provided greater timeliness, precision and damage assessment for commanders than cyber weapons did. With cyber weapons, you don’t always know if an attack has succeeded or been patched. But with explosives, you can see the impact and assess the damage more easily.

Finally, the most important lesson is also one of the oldest: war is unpredictable. As Shakespeare wrote ^[28] more than four centuries ago, it’s dangerous for a leader to ‘cry “Havoc!” and let slip the dogs of war’’ The promise of a short war is perilously seductive. In August 1914, European leaders famously expected ^[29] the troops to ‘be home by Christmas’. Instead, they unleashed four years of war, and four of those leaders lost their thrones. Immediately following America’s 2003 invasion of Iraq, many in Washington predicted a cakewalk (‘Mission Accomplished ^[30]’ read the warship banner that May), but the effort bogged down for years.

Now it is Putin who has let slip the dogs of war. They may yet turn on him.