On 24 August 2014, troops of the rebel Donetsk People’s Republic launched an offensive south of the city of Donetsk in Eastern Ukraine. They rapidly tore a huge hole in the defences of the Ukranian Army, surrounded some 4,000-5,000 Ukrainian troops, and advanced southwards towards the city of Mariupol.

Facing catastrophe, the Ukrainian government sued for peace, and the warring parties agreed to a ceasefire on 5 September. Although there has been some heavy fighting since then, the frontlines have remained largely unchanged. What were the causes of the rebel victory?

There can be no doubt that the rebels received military supplies from Russia. The content and scale of this aid is unknown, but it seems probable that it was more in the form of smaller items which could be easily concealed, such as anti-tank missiles, man-portable air defence systems, ammunition, uniforms, medical equipment and fuel, rather than big-ticket items such as tanks and artillery pieces. The rebels captured many of the latter from the Ukrainian Army.

The rebels also benefitted from the presence of several thousand Russian volunteers in their ranks. Most of these were formerly civilians, but they included some members of the Russian Army on “extended leave,” which undoubtedly had official approval. In addition, there is some evidence to suggest that Russian artillery sometimes fired across the border at Ukrainian targets. Accusations that large units of the Russian Army crossed into Ukrainian territory cannot be verified, however.

The Russian support for the rebels was crucial. That said, at the time of the August battles, the Ukrainian Army had about 50,000 troops in the theatre of combat operations, whereas the rebel force (created out of nothing in April) was only about 20,000 strong. The disparity in heavy equipment was even greater, the rebels having around 100 armoured vehicles and the Ukrainian Army perhaps 600. Even with Russian support, the rebels were still outnumbered and outgunned. Russian assistance alone does not explain their success.

The rebels were more highly motivated than their opponents. All of them were volunteers, and most were locals who believed that they were defending their homes. By contrast, most of the Ukrainian troops were conscripts, and Ukrainian morale was fragile.

Next, the rebels enjoyed the advantage of interior lines of communication. This enabled them to move reserves rapidly from one threatened sector to another, and so withstand the Ukrainian attempts to cut the area they controlled in half.

Most important, though, were errors committed by the Ukrainian Army. Too much effort was put into seizing territory and planting the Ukrainian flag, and not enough into destroying the enemy’s army. Rapid pushes into enemy territory without regard for flanks led to repeated encirclement.

The most striking error was an offensive in late June along the Ukrainian-Russian border south of the cities of Donetsk and Lugansk. The objective was to cut the rebels off from their Russian supplies. The actual result of the offensive was to place several thousand Ukrainian troops at the end of a very narrow corridor between Russian and rebel-held territory. The rebels were able to interdict supplies moving down this corridor, and then in mid-July to cut the corridor entirely, so surrounding the Ukrainians. While some troops eventually escaped, many hundreds were killed, wounded or captured. The rebels also captured a significant amount of heavy equipment.

The Ukrainian Army repeated the same mistake in late July when it attempted to cut the rebel-held territory in half by means of long, narrow pincers thrust from north and south towards the town of Shaktyorsk. Using their internal lines of communications, the rebels were able to rush reinforcements to thwart the Ukrainian plan, and the Ukrainians saw their forces at the end of the pincers cut off and destroyed. In mid-August, the Ukrainians tried the same strategy again with an offensive from north and south towards the town of Krasnyi Luch. This too was defeated.

Advances by the Ukrainian Army in July and August created a perception that Ukraine was winning the war. This perception was false. Although it lost ground, throughout this period the rebel army continued to become a stronger force. The constant shelling of Eastern Ukrainian towns by the Ukrainian Army helped to alienate the population and persuaded more and more people to join the rebel ranks, which gradually also became better and better equipped as they captured Ukrainian equipment and received Russian donations.

Clausewitz pointed out that the aim of war is to destroy the enemy’s army. By focusing on capturing territory, the Ukrainians failed to do this. This sealed their fate.
Paul Robinson is a Professor in the Graduate School of Public and International Affairs, University of Ottawa. He served as a regular officer in the British Army Intelligence Corps, and as a reserve officer in the Canadian Armed Forces.