Among the three armies in the region, the strongest—the Italians—were the first to make a move, which came as a minor surprise.
While Model was engaging the Italians in the Alps, Mainz led the main German army to confront remnants of the former Austro-Hungarian forces in austria.
Although this army, composed of Balkan and other regional units, numbered around 150,000 men, it was far from unified. The largest group was the Zeke people with 50,000 men, Slovenia and Croatia each contributed roughly 40,000, and Servea had the fewest at just 10,000 soldiers.
Upon learning this, Mainz immediately made a decisive plan: annihilate them completely.
On October 1, the Germans launched an attack on the Servians entrenched south of Vienna.
The Serbian army was a shadow of its former self. Historically, Serbia had played a key role in triggering the First World War, but following the war, Allied forces invaded, destroyed the country, and annexed parts of it to the Austro-Hungarian Empire. Puppet armies had been installed to suppress local resistance.
After Austria-Hungary's defeat, most of these armies were disbanded, but some soldiers remained stranded in austria. Among them were 20,000 Serbian who had committed numerous atrocities in their homeland. Returning home was too dangerous; they feared reprisal from their own government.
The Austrian authorities, unable to expel these former Austro-Hungarian troops, were forced to feed and supply them to prevent further trouble. Yet these troops were poorly disciplined, inexperienced, and often behaved more like bandits than soldiers—allowing prostitutes into barracks openly and showing little respect for military order.
"The army is no longer an army—it's a gang of criminals," Guderian noted eagerly. "Colonel, give me two regiments, and I can wipe them out!"
Mainz shook his head. "Even if two regiments could handle them, our goal is not simply to defeat them—we must annihilate them completely. We cannot let news leak and alarm the other armies. We must uproot them with precision and force."
Seeing Guderian hesitate thoughtfully, Mainz continued:
"In war, it is better to cut off one finger than to injure ten. Annihilating the enemy's manpower is essential to winning the war. Weapons, ammunition, aircraft, and artillery all require people to operate them, and every young, strong individual lost is a blow to the enemy's war potential.
"When facing a capable enemy, we must aim to destroy their entire army wherever possible. That way, even if the enemy quickly trains new troops, they will be inexperienced rookies. You all know the difference: a veteran with battlefield experience versus untrained recruits is a massive advantage. If we continuously destroy the enemy in successive battles, their experienced forces are eliminated, and they cannot gain combat experience. This ensures a permanent edge, which can be leveraged to achieve ultimate victory."
Mainz's strategy reflected the lessons learned from the German army in World War II. At the war's start, German forces were nearly unstoppable. In both Western Europe and on the Eastern Front, they annihilated enemy units before the opposition could adapt. The enemy had no chance to learn or adjust.
This advantage allowed the Germans to achieve astonishing results, destroying hundreds of thousands—even millions—of enemy troops. Though the Soviets mobilized tens of millions, most were inexperienced recruits, and their combat effectiveness could not match the seasoned German veterans.
However, all of this changed with the harsh winter and heavy snowfall near Moscow. The weather slowed the German advance, giving the Soviet army time to adapt. They learned German tactics, exploited weaknesses, and leveraged their vast manpower and industrial capacity, eventually establishing an advantage that persisted until the end of the war.