These rivalries sometimes remained cold but other times turned hot. What many of them had in common was stabilization – either to keep a cold peace or to end a hot war – through arms control.

Conventional Arms Control (CAC) became a modern, international institution at the end of World War One, and has been a fixture since then. It came into its own at the end of the First World War when the defeated central powers were subject to rigorous military limitations and – going beyond keeping defeated dogs muzzled – states collaborated to prevent future conflicts by reducing some of the potential causes of war through demilitarization of land and sea areas that might otherwise compel one rival to seize strategic or contested areas to deny its possession by another rival.

Adversarial CAC – of which there have been some 40 agreements from 1918 to the present, with many agreements still in effect today – is, by definition, between rivals. These agreements have been made between rivals who have had historical disputes spanning centuries or who may have just had a conflict that resulted in large-scale death and destruction – and even ethnic cleansing and genocide. They are agreements between states who have deep distrust for one another at best and deep hatred at worst.

What CAC does, however, is lock in the existing status quo so adversaries do not need to engage in arms racing out of fear of their adversary upsetting the status quo. Moreover, it can, depending on the monitoring and verification regime, increase transparency so that states have greater confidence that an adversary is not preparing a surprise attack. One of CAC’s side benefits is that states can allocate resources to other priorities – including aspects of their military not subject to arms control agreements.

Adversarial CAC is an important international relations tool whenever there has been, is, or may be a rivalry. It is a tool that has been more successful than less in helping prevent terminated conflicts from recommencing and preventing wars from breaking out in the first place. It has even helped turn rivals into friends. In a time in which there is deep mistrust between the EU-Ukraine coalition and Russia, many would question why and how arms control can be an option.

It is, however, not just an option. It’s probably the best option for preventing what no one wants – not even President Putin – a general, continental war in Europe. As scholars of war would most certainly concede and even President Putin cannot deny – wars are often unpredictable and costly. Even President Trump is feeling this axiom’s stings as he attempts to negotiate a peace with Iran that in no way amounts to a Tehran unconditional surrender.

A CAC agreement or set of agreements between the EU, European NATO members and their security partners, such as Ukraine with Russia, would have many benefits. In its broadest forms, CAC would do what it has historically done – limit or end arms racing, offer transparency and predictability through on-site inspections and clear rules against concealing weapons, and offer an avenue for regular military exchanges and diplomacy that can contribute to improving diplomatic relations.

There are two broad categories of arms control: national limitations, in which one or more parties’ military capabilities are subject to limitations across their entire national territory and beyond (for example, setting a limit on the number of tanks or combat aircraft a country can have); and geographic demilitarization, in which a specified geographic area is subject to limitations of at least one state’s military capabilities, but not beyond that area (for example, prohibitions on military forces on Finland’s Åland Island). Agreements between the EU/NATO and Russia should likely include both approaches – and in fact some agreements are already in place, and have been so for over 100 years. Future agreements might include limiting the number of combat aircraft each side possesses, the number of naval vessels present in the Baltic Sea, the location of drones over a certain weight, or even the number of active-duty military personnel.

Sometimes, CAC is not a choice. Over the past 100 years, CAC has been integral to armed conflict termination. Indeed, all indications are that any end of the Russo-Ukrainian War will involve arms control. Moreover, a broad and continuous European NATO/EU rearmament program would likely and eventually be matched by commensurate Russian arming and deployments, thus resulting in no net gain in European security but high financial and opportunity costs.

Thus, the EU as an institution should prepare itself for a future of adversarial arms control – much like the Cold War period before the EU existed. This might involve expanding and elevating the EU arms control office, preparing to engage in rigorous monitoring and verification activities, and researching arms control agreement options. EU arms control efforts might be greeted with deep distrust by EU citizens, experts, and national officials because of Russia’s recent history of aggression and perfidy – but if the absence of arms control increases the risk of war, then arms control must be pursued.

About the author:

Dr. William Lippert received is PhD from Leiden University, Netherlands, in October 2025. His dissertation was focused on adversarial conventional arms control (CAC) in Europe, and based in part on empirical analysis of approximately 30 CAC agreements in Europe from 1918-2015. Prior to his PhD work, William was a career intelligence analyst at INTERPOL and the US Department of Defense.

This blog post is part of a series of contributions in the context of EURISGA – The European Union’s Role in Security and Global Affairs. It is a Jean Monnet Chair funded by the European Commission (Grant Agreement Number: 101085789).