Europeans approached Russia’s war against Ukraine with their usual passivity: deferring to the United States to define strategy and contributing only proportionally to GDP. Despite a widespread understanding of the catastrophic consequences of a Ukrainian defeat for Europe, this awareness did not spur a serious mobilisation of defence industries, training, and support efforts necessary to secure victory.

This was a grave mistake. As Donald Trump prepares to take office, the prospect of dwindling military assistance to Ukraine looms large, leaving Europeans with few options to intervene at this late stage.

US military support is not only the largest in absolute terms – though only a fraction of the promised assistance has actually been delivered – but the ammunition and systems it provides cannot be easily replaced on short notice. For example, the US produces more surface-to-air missiles than Germany, France, and Japan combined, and without US approval, not even German-built Patriots can be sent to Ukraine. With Russia throwing more than 1,200 missiles per year at Ukraine, the entire production capacity of surface-to-air missiles in the Western world would be needed to meet the demand. If the US were to deprioritise Patriot deliveries to Ukraine, the country’s air defence efforts would be in great trouble. If deliveries were halted, it would certainly collapse.

Other munitions, such as the GMLRS rockets for HIMARS and the M270 rockets, are produced exclusively in the US; setting up production licenses in Europe would take time. And if the US suspended technical support for the Ukrainian air force, the ongoing transition to Western fighters (predominately F16s) would suffer as well.

The US is also Ukraine’s primary source of armoured fighting vehicles, having delivered more than 300 of a total of 780 infantry fighting vehicles provided, and over 1,300 out of the 2,200 armoured personnel carriers. As European stockpiles of older vehicles (both Soviet and Western design) deplete, US reserves could become the last lifeline for Ukraine’s mechanised forces in the latter half of 2025, assuming they are available then. Only in artillery shell production Europe surpasses the US – 600,000 against 480,000 annually, respectively. However, to supply Ukraine with the minimum 1.8m shells a year it needs for defence, both the US and Europe rely on third countries.

Despite the crucial role of the US, the Biden administration has struggled to clearly define war aims. Military supplies have proven insufficient for Ukraine to merely hold the line, let alone seize initiative and apply enough pressure on Moscow for serious negotiations. The Ukrainian armed forces have faced many periods of high casualties, some due to their own mistakes, like the prolonged defence of Bakhmut; others caused by the West’s shortcomings, like the shell shortage period in the spring of 2024. Together, these factors have severely eroded the qualitative edge Ukraine once had over Russia, as many of the highly motivated soldiers with experience in the Donbas, who formed the bulk of the land forces in the beginning of the full-scale invasion, have died.

Now Ukraine risks going through another period of shell hunger and supply shortages while Trump is busy reshaping the country to mirror his ideological leanings, coupled with the usual revanchism against political and administrative elites. For a while at least, Ukraine will be a secondary, if not tertiary concern for the new president.

What Europe can do in the face of the impending catastrophe

Europeans could purchase equipment and ammunition from the US, shifting costs to the EU budget – that is, if the US is willing to sell. Trump could also tie military assistance to political concessions from the EU, such as refraining from retaliating against US tariffs, or side with the US on economic issues at the expense of European interests. Such a dynamic would create a far more toxic relationship than merely shouldering financial burdens. EU member states could have secured long-term delivery contracts with the US while Biden was still in office. But now it is too late; the US export bureaucracy needs time to clear the usual technicalities.

In theory, the European governments could keep Ukraine afloat by delivering armoured fighting vehicles and aircraft from its own inventories. But given Trump’s occasional outbursts and threats to not defend European allies against Russia, as well as his unpredictable policies, European states might not want to part with their own defence stocks. The only glimmer of hope in this mess is Ukraine’s defence industry, which is poised to considerably increase production and develop a variety of new weapon systems by next year – but only if it can be protected from Russian missile strikes.

Europeans also need to consider that rebuilding battering Ukrainian units involves not only providing materiel, but also training. Weaknesses in training, human resource management, officer and staff-officer training, and doctrinal adaption have become evident as losses mounted and less experienced soldiers and officers have been pushed to fill roles in an expanding force. Europeans should take French president Emmanuel Macron’s proposal of sending advisors much more seriously than they have so far.

Beyond these potential solutions, Europeans must not underestimate the gravity of the long-term scenario. No one knows what Trump’s “plan” for Russia’s war in Ukraine entails – beyond his promise to end it “within one day” – but a slowdown in military assistance will put Ukraine in such a precarious and unpredictable situation in 2025 that Moscow will have even fewer incentives to come to the table. After all, why should Putin concede in talks what he can gain on the battlefield, likely at lower costs? Putin may well engage in a negotiation “process” to win favour with Trump, while he diverts attention from military supplies and buys time to advance militarily. But nothing of substance should be expected from these talks. It is important to recall that the first Trump administration had an extremely weak track record in compelling adversaries – Iran and North Korea in particular – to comply or seriously engage with its agenda. In general, Trump hesitated to apply meaningful pressure on them out of fear of domestic repercussions. There is no reason to believe he will fare better this time around.

What may lie ahead for Ukraine

The most optimistic scenario is that Ukraine manages to secure sufficient supplies and endures into 2026 with minor territorial losses. If Russian casualties remain high, Moscow may seek an operational pause by the end of 2026 or in 2027 to replenish stocks and reorganise. Given the growing war weariness in Ukraine, Kyiv would probably take a pause then. But as Ukraine joining NATO – the only security guarantee Russia would respect – seems highly unlikely under Trump, a ceasefire would not mean peace, but a Donbas-style, low-intensity war across a 1,200 kilometre front, with frequent missile and drone strikes terrorising Ukrainian civilians.

The most pessimistic scenario is, of course, the erosion of Ukraine’s battered land forces leading to a collapse of the front, or of the organised military resistance itself. Russia may then execute its long-anticipated plans to seize political control and exterminate the political, intellectual, and administrative elites of Ukraine, along with the nation itself. Involving Russia’s large domestic security apparatus in this war of annihilation, accompanied by the resettlement of loyalists in the new Lebensraum, would further cement the aggressive, anti-Western, militarist regime in Russia. Its imperial ideology and foreign policy would extend far beyond the lifespan of Putin.

For Moscow, the conquest of Ukraine is not the end goal, but a necessary step towards re-establishing Russia as a great power. Its ambition is to revise the entire European security order, driving the US out of Europe and a having a militarily dominant Russia dictate European political affairs at will. Trump’s erratic behaviour on NATO and his disdain for allies could provide Russia with openings to pursue these aims far beyond Ukraine. In this precarious moment, an ill-prepared Europe has run out of time to bolster its defences. By wasting three critical years not supporting Ukraine decisively and preparing for a potential Trump return, Europe has sown the seeds of its own Untergang, or downfall. Russia will reap it.