Introduction
In October of 1648, Swedish forces launched a daring assault on Prague, storming its fortifications while Imperial defenders fought desperately to hold the city. Artillery thundered across the Vltava River as disciplined infantry formations clashed in the streets.1 The battle was brutal yet indecisive; it concluded not with total destruction but with news that diplomats in Münster and Osnabrück had negotiated a settlement. The Peace of Westphalia did more than end the Thirty Years’ War; it redefined sovereignty, codified State monopoly on violence, and laid the foundation for the modern international order.2 This centralisation of power became the catalyst for military evolution. Only the State possessed the resources to field massive standing armies and sustain industrial mobilisation, which would characterise subsequent eras of conflict.3
From this state-centric foundation, military theorists have traced the evolution of conflict through five distinct generations, summarised in Table 1. First-generation warfare (1GW) emphasised massed manpower; second-generation (2GW) relied on industrial firepower; third-generation (3GW) prioritised manoeuvre and speed; and fourth-generation (4GW) eroded the state monopoly by introducing non-state actors and insurgency.4,5 To this spectrum, scholars now add a theoretical fifth-generation (5GW), which moves beyond physical violence to incorporate grey zone conflict and cognitive manipulation.6 While scholars debate the precise boundaries of these generations, the operational reality for NATO is that contemporary adversaries do not select one ‘generation’ at a time. The defining characteristic of the modern battlespace is the simultaneous convergence of all five generations of warfare.
Table 1: Generations of Warfare.
This convergence is clearly seen in the Russia–Ukraine war, where the battlespace defies categorisation. Russia continues massing soldiers, employing massed artillery barrages and employing drones from trenches, executing manoeuvre operations on land and in the air, utilising mercenaries such as the Wagner Group, and shaping public discourse through information operations, as illustrated in Figure 1, on page 52.7,8
Figure 1: Russia’s MGW modalities.24 © Russian Hybrid Warfare modalities. Concept adapted from Mark Voyer’s ‘RUS Hybrid Warfare “Hydra”’. Graphic recreated by JAPCC.
This Multi-Generational Warfare (MGW) environment strains NATO’s traditional deterrence model. The Alliance is structurally optimised for state-on-state kinetic aggression, yet it now faces adversaries who blend industrial warfare with non-kinetic campaigns to exploit the seams between peace and war. NATO must adapt its deterrence model to this multi-generational reality. The Alliance must integrate non-kinetic domains, irregular warfare, and grey-zone resilience into a coherent framework, while simultaneously maintaining the capacity to fight and prevail in the high-intensity conditions of previous generations. The following sections analyse the evolution of the battlespace, assess the gaps in NATO’s current kinetic-focused posture, and propose an integrated deterrence framework that spans the nuclear, conventional, and grey zone spectrum.
The Evolution of the Battlespace
1GW reflected the dawn of the nation-state, relying on massed rank-and-file formations meeting at predetermined times and places. Battles such as those in the English Civil War and Napoleonic Wars were highly controlled and confined to the visual battlefield, where victory often depended on sheer manpower and casualty counts.9
This paradigm was shattered by the industrial revolution, and 2GW emerged as rifled muskets, machine guns, and artillery rendered traditional rank-and-file formations suicidal. It was a linear but bloody transition; the early years of World War I demonstrated the lethality of applying 1GW tactics against 2GW technology. In response, armies reduced formation depth, increased width, and relied on centralised, indirect fire to destroy the enemy through attrition.10
3GW broke the stalemate of attrition by establishing manoeuvre and tempo as central to operational success. This approach required decentralised execution, high-readiness forces, and the ability to outmanoeuvre an aggressor to shatter both their physical and psychological cohesion. World War II epitomises the birth of 3GW, with dispersed operations and deep penetrations across vast theatres.11
It was within this 3GW paradigm that NATO found its footing. The Alliance’s deterrence posture during the Cold War represented the apex of this model, designed to counter a massive Soviet invasion across the Fulda Gap through superior manoeuvre and rapid reinforcement. However, the post-Cold War era fostered an assumption that high-tech quality had permanently replaced quantity, leading to divestment in mass and the belief that previous generations of war were obsolete.
4GW dismantled this assumption by ending the State’s monopoly on war. Emerging prominently after the collapse of the Soviet Union and accelerating after 9/11, 4GW demonstrated that tactical victories and superior firepower no longer guaranteed strategic success. State militaries found themselves engaged with violent extremist organisations (VEOs) and sub-state entities that made political will, rather than terrain, the decisive objective.12 By expanding conflict into political and social spheres, as seen in the decades-long struggle in Afghanistan, weaker actors circumvented conventional military dominance to impose decisive costs beyond battlefield attrition.13
5GW, or grey-zone conflict, further dissolves the lines between peace and war. While 4GW introduced non-state actors, 5GW sees State actors weaponising ambiguity. This shift became undeniable during the 2014 annexation of Crimea, where ‘little green men’ achieved strategic goals without triggering a conventional response. Beyond land, sea, air, and space, 5GW targets politics, culture, values, data, leadership, morale, and perceptions.14 Its central aim is to ‘win without fighting’ – a principle long articulated by Sun Tzu – by operating below the West’s recognised threshold of armed attack. As illustrated in Table 2, adversaries employ a spectrum of non-military tools, from economic coercion to legal warfare. These methods underscore the complexity of 5GW, where victory hinges on shaping narratives and eroding trust rather than seizing terrain.
Table 2: Types of 5GW described in ‘Unrestricted’. Published in 1999 by Beijing’s PLA Literature and Arts Publishing House.25
The Multi-Generational Reality: Convergence and Simultaneity
The defining challenge of the contemporary security environment is not the existence of these five generations, but their simultaneity. In the past, military theory assumed a sequential progression from one generation to the next. Today, that logic is obsolete. Adversaries do not select a single generation of warfare. They employ an MGW strategy that additively applies capabilities to exploit specific vulnerabilities. For NATO, this presents a dilemma in generating an appropriate response. An adversary may use 5GW modalities to destabilise a region politically, avoiding attribution, while simultaneously massing 2GW artillery on the border to deter intervention and threaten high operational costs. This ‘full-spectrum’ approach is designed to paralyse decision-making by overloading the defender’s ability to classify the threat. Is it a riot? Is it an invasion? Is it a diplomatic crisis? By the time NATO categorises the threat, the adversary has often already achieved its objective.
The Strategic Gap: Kinetic Deterrence in a Grey Zone World
This multi-generational reality exposes a structural fissure in the Alliance’s deterrence posture. NATO’s current framework remains optimised for high-intensity, state-on-state conflict, leaving it firmly anchored in the legacy of 3GW and the Cold War era. The Alliance’s 2022 Strategic Concept reaffirms a posture built on nuclear capabilities, forward-deployed conventional forces, and collective defence under Article 5.15 While these pillars remain essential for preventing a 3GW operational collapse or nuclear escalation, they are ill-suited for the lower-intensity spectrum of 4GW and 5GW. NATO’s deterrence model is largely binary. It is designed to switch from peace (white) to war (black) upon the triggering of Article 5. Adversaries understand this threshold and deliberately operate below it, creating the grey zone gap. Actors such as Russia exploit the ambiguity of 5GW to achieve strategic gains without ever tripping the wire of collective defence. Crucially, this grey-zone strategy is directed against NATO’s political centre of gravity, namely the consensus model. Article 5 is a political decision, not an automatic trigger. By operating in the realm of ambiguity 5GW represents, adversaries obscure the attribution required to generate political consensus among 32 nations. If the Alliance members cannot agree on who is attacking NATO, it cannot hope to agree on how to respond.
NATO leadership has recognised this vulnerability. Recent strategic advances, such as the Concept for Deterrence and Defence of the Euro-Atlantic Area (DDA) and the NATO Warfighting Capstone Concept (NWCC), clearly identify these hybrid threats and emphasise a ‘360-degree’ approach to security. However, while the concepts are sound, the Alliance’s practical toolkit for responding to non-kinetic aggression remains underdeveloped when compared to its robust kinetic warfighting plans. This leaves a gap where adversaries can manoeuvre with relative impunity, confident that their actions will not generate the clarity required to trigger a unified Alliance response.
Adapting the Framework: A Functional Approach
NATO’s adaptation must move beyond a simple shopping list of capabilities. To deter effectively across multiple generations of warfare, the Alliance requires a functional framework that organises its response into three distinct pillars: Orchestration, Resilience, and Contestation.
1. Orchestration: Solving the MDO Challenge
The primary challenge of MGW is the sheer volume of activity. NATO must accelerate the implementation of its Multi-Domain Operations (MDO) concept to act as the central nervous system for the MGW environment.
- Civ-Mil Integration: MDO, by its nature, is not purely military. In 5GW, the ‘terrain’ is often civilian owned, including digital banks, energy grids, and social media platforms. Therefore, NATO’s command and control must integrate civil and military data streams to visualise the 5GW battlespace.16
- AI-Enabled Speed: Orchestration requires processing power. Leveraging artificial intelligence for predictive analysis will allow commanders to sift through the noise of hybrid campaigns and identify the adversary’s main effort, yielding an operational tempo advantage.17
2. Resilience: The ‘Shield’ of Deterrence
To deny adversaries the easy gains they seek in the Grey Zone, NATO must harden the soft targets of democratic society to achieve deterrence by denial.18
- Layered Resilience: Deterrence is no longer just about tanks on the border. It is about the ability of a society to absorb shock. This requires a wide range of civilian structural changes, such as hardening critical cyber networks, securing transport and energy infrastructure, and strengthening supply chains.19
- Cognitive Defence: Resilience must extend to the mind. Adversaries militarise information to fracture Alliance cohesion. Countering this attack vector requires proactive and persistent strategic communications and meaningful education, rooted in Western values, which inoculates populations against disinformation before it takes root.20, 21
3. Contestation: The ‘Sword’ in the Grey Zone
Finally, NATO must close the grey-zone gap. Deterrence fails if the adversary believes NATO has no response options short of total war.
- Irregular Warfare Capabilities: NATO must institutionalise irregular warfare competencies. Special Operations Forces (SOF) and intelligence elements must be empowered to compete in the grey zone by conducting counter-proxy operations and exposing adversary activities without necessarily triggering a full kinetic war.22
- Attribution as a Weapon: The greatest enemy of 5GW is transparency. NATO must invest in rapid attribution mechanisms that strip away the adversary’s plausible deniability. By publicly attributing cyber or hybrid attacks quickly and accurately, NATO denies the enemy the ambiguity they need to fracture political consensus.23
Conclusion
The MGW framework is not merely an academic construct. It provides a vital diagnostic lens for reevaluating the Alliance’s security posture. While NATO remains well-prepared to counter the high-intensity kinetic threats associated with earlier generations of warfare (1GW – 3GW), its resilience is increasingly tested by the simultaneous convergence of contemporary challenges. In this evolving environment, adversaries exploit the ambiguity of 5GW, weaponising subtlety to circumvent NATO’s established strengths and undermine Alliance cohesion. To navigate this complex landscape, NATO must move beyond incremental capability upgrades and embrace a functional framework for integrated deterrence. This evolution should rest on three interdependent pillars: orchestration, resilience, and contestation. Orchestration will enable the Alliance to manage the simultaneity of the modern battlespace, synchronising effects across kinetic and non-kinetic domains through MDO. Resilience will deny adversaries the easy wins of 5GW by hardening the societal and digital foundations that underpin military power. Contestation will ensure NATO can compete effectively in the grey zone, imposing costs on adversaries before they escalate to armed conflict. Ultimately, a multi-generational approach that integrates nuclear, conventional, and grey-zone instruments is essential to restoring deterrence credibility. By doing so, NATO will reaffirm its role not as a relic of the Cold War, but as the cornerstone of Euro-Atlantic security for decades to come.
