General Nick Carter is the former U.K. Chief of the Defence Staff. He is a strategic counselor at the Tony Blair Institute for Global Change.

Defense ministers, senior military officers and industry leaders are gathering in London this week for the Defence and Security Equipment International (DSEI), claimed to be the world’s largest military expo. But while the DSEI offers a glimpse into the future of warfare, showcasing the latest technologies, Europe’s real test isn’t innovation in theory — it’s whether it can mobilize fast enough in reality.

As the Atlantic Council recently put it, Europe’s problem until now has been its political and military unwillingness to rise to the challenge. But with Washington wavering and Moscow menacing, the continent is at a strategic juncture, faced with the choice of assuming responsibility for its own defense and security, or remaining dangerously dependent on forces beyond its control.

What’s in doubt is whether growing common cause among European leaders and significant increases in European defense spending can unfold quickly enough to save Ukraine without significant help from the U.S. It also remains to be seen if these factors can restore deterrence in the Euro-Atlantic area to discourage a Russian threat materializing before 2030.

These days, deterrence must also account for the so-called “grey zone.” Russia is already eroding NATO’s Article 5 commitment to mutual defense through attacks that fall into this hybrid category, all designed to weaken resolve without triggering a conventional military response. And it is likely to escalate such calibrated provocations including, for example, undersea cable sabotage, cyberattacks on power grids or missile “accidents” near NATO territory. All this is a deliberate strategy to expand Moscow’s influence.

Meanwhile, on the battlefield in Ukraine, we’re seeing a mix of World War I and World War III — a real-time case study foreshadowing some aspects of future warfare. Over the last few years, we have witnessed how fast the character of conflict evolves, and how the boundaries between land, sea, air, space and cyberspace fade as we seek to integrate these domains for advantage.

Here, many rightly point to Ukraine’s ingenuity in adapting under fire, but Russia has innovated at equal speed and scale: deploying cheap drones, electromagnetic jamming, AI-enabled targeting and retooling its economy into an engine of war. This year alone, the country will produce 1,500 tanks, 3,000 armored vehicles and 200 ballistic missiles — matching NATO’s annual output in a matter of months.

Given this pace of technological change, keeping abreast of innovation is critical, and Europe’s defense planning must be built on that principle. In warfare, the side that adapts fastest has always had the best chance of winning — not least, as military historian Sir Michael Howard observed: “Everybody gets it wrong so the important thing to do is to develop the intellectual capacity to adjust faster than the other guy.”

But Europe needs a fundamental rethink — not only of the capabilities required both now and in the future, but of how its systems and institutions must change to deliver them. This means scaling up defense production, modernizing forces, rethinking procurement and investing in the right mix of capabilities for today’s threats, as well as those on the horizon.

To address this, the Tony Blair Institute will initiate a program to encourage discussion on European defense, looking at the security landscape and the potential scenarios that could unfold. We will discuss burden sharing, including roles, regions, capabilities and the defense-industrial base, and we hope to initiate a debate on national and societal resilience.

Thankfully, Europe is working off a a stronger foundation now that non-U.S. NATO members have pledged to lift core defense spending to 3.5 percent of GDP, and the EU has launched its €150 billion Security Action for Europe (SAFE) fund to boost defense capacity. But these steps will fall short if the money isn’t spent quickly.

And yet, the U.K. admits it won’t hit its target until 2035, and Spain refuses to commit at all. Moreover, according to the International Institute for Strategic Studies, SAFE is dwarfed by the $1 trillion that will be needed to close Europe’s capability gaps if the U.S. were to pull back.

Amid all this, the unspoken truth is that more money alone isn’t enough: Without strategy, political resolve, national resilience and structural reform, investment won’t translate into real capability.

Too often, defense spending is treated as an industrial jobs program rather than a security imperative. But governments must be honest with their citizens: Higher defense spending will mean hard trade-offs.

Today, polls show that even though half of Britons expect a world war within a decade, only a third support raising defense budgets if it means higher taxes or cuts elsewhere. And while Europe needs to be aiming for at least 3.5 percent of GDP on defense, even this level of spending will fall short without procurement reform and a wartime mindset in industry.

DSEI will display the technologies shaping tomorrow’s battlefields, but the real question is whether Europe has the will, speed and coordination to turn those technologies into credible deterrence.

Our economies are 10 times the size of Russia’s, our technological base is vastly stronger, and our alliances are unmatched. If we choose to act with urgency, then any threat from Russia can be dealt with.

The question is whether we will.