The Front Line North-East of Sumy

The stretch of borderland north-east of Sumy has long been one of the least understood yet most strategically revealing theatres of the Russo-Ukrainian war. Since the opening months of 2024, Ukrainian light infantry, supported by special forces and irregular volunteer formations, had established and maintained a precarious salient inside Russia’s Kursk oblast. For many months this outpost was treated by Kyiv not primarily as an attempt at territorial conquest, but as a means of shaping the battlefield: disrupting Russian logistics, imposing strategic ambiguity upon Moscow, and demonstrating that Ukraine retained the initiative even whilst confronting overwhelming Russian mass elsewhere. By late 2025, however, the position had transformed. The salient that once appeared to symbolise Ukrainian audacity was steadily constricted, the Russians having re-committed mechanised forces to reassert control of their own border districts. The front line north-east of Sumy is now an unstable seam in which both armies confront the limits of endurance, and in which the earlier Ukrainian presence inside Russia has left deep political echoes.

The origins of this Ukrainian advance lay in Russia’s partial reallocation of experienced troops to the central Donbas axis during 2023 and early 2024. Border areas of Kursk and Bryansk had been garrisoned only lightly, often by poorly trained conscripts with limited artillery support. The Ukrainian Armed Forces identified this vulnerability and mounted a series of raids expanding gradually into semi-permanent positions across a number of villages and forested tracts. The objective was not to precipitate a deeper drive into Russian territory, which Kyiv neither desired nor possessed the manpower to support, but to fragment Moscow’s operational picture. Each kilometre gained inside Kursk imposed a dilemma upon Russian commanders: either to divert seasoned battalions away from critical fights in the east, or to endure a Ukrainian presence threatening nearby logistics nodes, roadways and ammunition dumps. For a time Russia chose the latter, gambling that Ukraine lacked the reserves to sustain such excursions indefinitely.

During mid-2024 the Ukrainian salient reached its greatest extent. It was held by mixed detachments whose professionalism often exceeded their numbers. Their operations remained fluid, blending reconnaissance, ambush activity, and controlled occupation of settlements that Russia appeared incapable of retaking at acceptable cost. These incursions carried a psychological weight disproportionate to their scale. They demonstrated that despite missile barrages, relentless assaults in Donbas, and Russian advances along the Kharkiv border, Ukraine could still penetrate Russian lines and impose new complications upon the Kremlin. For Ukraine’s allies, the message was one of resilience and continued operational sophistication. For Russia, the embarrassment was acute: a nuclear power that could not fully defend her own frontier.

The mood shifted decisively in late 2024 and early 2025. Russia began belatedly to recognise that the political costs of tolerating a Ukrainian enclave on her territory outweighed the short-term operational advantages of concentrating elsewhere. Reinforcements arrived from Russia’s eastern military districts, accompanied by heavier armour and increasingly aggressive aviation sorties. The Kremlin also directed her artillery to saturate border settlements, notwithstanding the risk of civilian casualties on her own soil. The Ukrainian positions, never deeply fortified and reliant upon thin supply lines threading from Sumy, became progressively less tenable. Winter compounded the difficulties. Russia’s numerical superiority permitted a slow tightening of the noose, village by village, treeline by treeline, until only the most hardened Ukrainian detachments could continue to operate cross-border without intolerable risk.

By late 2025 the Ukrainian Armed Forces had withdrawn from most of their earlier footholds inside Kursk, preserving manpower and equipment rather than feeding an increasingly costly attritional struggle. Yet the consequences of that earlier presence remain significant. First, Russia has been compelled to maintain a much larger troop concentration along hundreds of kilometres of her western border. These battalions represent forces that cannot be committed to deeper thrusts in Donbas or Zaporizhzhia. Although Russia has attempted to push back into Ukrainian territory to create a buffer zone, she had only limited and temporary success. Secondly, Ukraine’s foray into Kursk demonstrated an operational truth that Russia would prefer not to acknowledge: that her border defences are permeable, and that sustained local superiority, even for a state fighting for survival, can impose real strategic effects inside Russia herself.

The present situation north-east of Sumy is one of tense equilibrium. Russia claims to have restored control over all lost territory in Kursk, but her grip is uneven. Ukrainian long-range drones, operating from within the Sumy forests, continue to strike Russian logistics further inland. Small reconnaissance teams are reported to cross the border periodically, gathering intelligence and seeking opportunities for sabotage. Russia for her part has constructed a deeper belt of fortifications, including trenches, anti-vehicle ditches, and electronic warfare posts designed to degrade Ukrainian communications. Artillery duels across the border have become routine. Civilians on both sides endure the consequences: intermittent shelling, disrupted harvests, and the constant fear of escalation.

For Ukraine, the withdrawal from Kursk does not signify failure but a recalibration of priorities. Kyiv’s leadership has increasingly focused upon defending the broader Sumy region from renewed Russian incursions, aware that Russia’s eventual aim may be a larger envelopment rather than isolated border raids. The Ukrainian Armed Forces are also redeploying experienced units from the Kursk operation to stabilise the front where Russian attacks remain most intense. Nevertheless the memory of the Ukrainian presence inside Russia continues to shape expectations. Should conditions permit—whether through a collapse of Russian cohesion, diversion of Russian reserves, or a sudden Ukrainian breakthrough elsewhere—the border north-east of Sumy could once again become a point of unexpected Ukrainian initiative.

Strategically, the salient’s rise and fall encapsulate several wider themes of the war. It demonstrates that Ukraine, even under severe strain, retains the capacity for innovation and audacity. It illustrates Russia’s chronic difficulty in allocating forces efficiently across her vast borders. It reveals how even modest territorial manoeuvres can exert psychological and diplomatic influence, challenging entrenched assumptions about the balance of power. And it serves as a reminder that this conflict has never been confined to the familiar front lines of Donbas alone; it reaches across borders, deep into the strategic imagination of both belligerents.

As winter settles over the forests and gently rolling farmland north-east of Sumy, the immediate fighting may appear quieter than the tumultuous months in which Ukrainian soldiers held the villages of southern Kursk. Yet beneath the frost lies a front line still alive with movement, observation and danger. The land remembers the presence of foreign troops, and the armies on either side know that this border remains one of the most symbolically charged in the war. Future operations may again transform it. For now it stands as a contested threshold: the place where Ukraine briefly carried the war onto Russian soil, and where the potential for renewed initiative endures, shaped by the hard lessons of the past two years.