German advances during the opening phases of Operation Barbarossa from 22 June 1941 to 25 August 1941 – public domain image map by the History Department of the US Military Academy

(6) ROMANIAN-SOVIET WAR

Now we come to the first of three active Axis combatants allied with Germany against the Soviet Union that, unlike the limited exceptions of Finland in the Winter War or Japan, were obviously subordinate to the German war effort and otherwise could not or did not fight the Soviets separately.

At first glance, it is somewhat surprising that Romania was first and foremost of these Axis combatants, given that Italy was Germany’s major ally in Europe. However, the primary theater of combat for Italy was always the Mediterranean, where Romania shared a border with the Soviet Union.

Indeed, the Romanian-Soviet border was a border across which Germany had ceded territorial concessions from Romania to the Soviet Union in the Nazi-Soviet Pact – the Romanian territory of Bessarabia, to which the Soviets also added Northern Bukovina and some islands in the Danube.

It was also a border across which Germany launched a major part of Operation Barbarossa, with Romania as allied combatant against the Soviets – both on land and in naval warfare on the Black Sea. And as combatant, Romania committed more troops to the Eastern Front than all of other Germany’s allies combined – with Romania apparently having the third largest Axis army in Europe (after Germany and Italy) and fourth largest in the world (after Japan as well).

Notably, like Italy and Japan, Romania switched sides from being on the Allied side in the First World War. Indeed, Britain had extended the same guarantee it made to Poland to Romania (and Greece) on 13 April 1939, prompted by the Italian invasion of Albania – such that Romania was effectively a potential ally to Britain until joining the Axis on 23 November 1940.

Romania’s significance in the Nazi-Soviet war and indeed to Germany in the Second World War was not just its military contribution, but also (and probably even more so) its economic contribution – primarily its oil, which saw Romania bombed by the Allies in their strategic bombing offensive against Germany.

Ultimately, as the tide of war turned against Germany, the war came to Romania itself in what has been dubbed the Battle of Romania – where the Soviets defeated German and Romanian forces before Romania surrendered and defected to the Allies, declaring war against Germany after a Romanian royal coup d’etat against the fascist government of Antonescu.

As historian H.P. Willmott observed, the German Sixth Army, reconstituted after the destruction of its predecessor at Stalingrad, eerily found itself replaying that destruction – as it was encircled and destroyed for a second time by Soviet forces when Romanian resistance crumbled (as before on its flanks at Stalingrad).

Romania then committed a substantial number of troops – which suffered substantial casualties – as combatants allied with the Soviets against Germany, not that either prevented the Soviet occupation of and installation of a subordinate communist state in Romania.

(7) ITALIAN-SOVIET WAR

Not surprisingly, as Germany’s major ally and only other Axis claimant to great power status in Europe, however inflated, Italy was also an active combatant allied with Germany against the Soviet Union.

Italy initially committed an expeditionary army corps, subsequently expanded into an army, to Germany’s campaign against the Soviet Union. Both saw action in the southern part of the Eastern Front – most notoriously in the fighting around Stalingrad, where Italian forces covering the German flank at the Don River bore the full brunt of the Soviet offensive to encircle Stalingrad.

Historian H.P. Willmott observed that the Germans considered the Italians the best of their allied combatants on the Eastern Front, although the competition for that accolade was not particularly fierce.

Almost all Italian forces were withdrawn from the Nazi-Soviet war as Italy’s primary theater of operations in the Mediterranean loomed larger with the Allied threat to Italy itself. Ultimately, that saw Italy as the first of Germany’s Axis allied combatants to surrender and defect to the Allies in 1943, although even then some residual Italian forces remained in the Eastern Front (serving on behalf of Germany’s puppet government installed in Italy).

(8) HUNGARIAN-SOVIET WAR

Hungary is the last of what I identify as the substantial Axis combatants allied to and participating in the German war against the Soviet Union – the others being Finland, Romania and Italy. Bulgaria was an Axis ally of Germany, but it was a special case as it did not declare war against the Soviet Union and remained neutral in that part of the Second World War. There were other Axis combatants that fought alongside German forces against the Soviets, but they were either small – at a divisional level or so – or consisted of volunteer forces rather than official participation, or both.

Hungary is also notable enough for its own entry, as it was also the last of Germany’s Axis allies to remain allied with Germany – albeit not so much by its own choice but because it was the subject of Germany’s last successful military occupation of the war in Operation Margerethe.

As such, Hungary itself became one of the last battlefields of the Second World War in Europe, with German and Hungarian forces fighting against the Soviets there into 1945, most notably in the Siege of Budapest. While the Ardennes Offensive or Battle of the Bulge was famously the last substantial German counter-offensive of the war, Germany did launch counter-offensives after that – with the last one that could be described as major in Hungary, the Lake Balaton Offensive in an attempt to secure Germany’s last source of oil and to prevent the Soviets from advancing towards Vienna.