The actions of the German army completely caught the Allies by surprise. Although the Allies had strengthened patrols along Austria's borders, the German troops disguised as locals still managed to slip through undetected.
Upon arrival in Vienna, Colonel Mainz immediately set to work organizing Austria's 50,000 troops, preparing them for the battles to come.
On September 21, 1919, while the Allied armies were engaged against Russia in Eastern Europe, the Austrian Congress officially passed a resolution overwhelmingly approving Austria's union with the German Empire—a historic event known as the German-Austrian merger.
The news quickly reached Berlin. Under pressure from the military, the Weimar Republic officially welcomed Austria's decision.
The Entente powers were stunned, but at that moment, their focus was entirely on Eastern Europe. They lacked the manpower to march through the Alps and intervene directly in Austria. Consequently, while applying diplomatic pressure, they encouraged the remnants of the former Austro-Hungarian army to form a coalition of five nationalities and march on Vienna.
This intervention force numbered around 200,000 men. In addition to the Balkan forces from the former Austro-Hungarian Empire, the Allies persuaded Romania to join. Romania, eager to claim land from Austria-Hungary now that the empire had collapsed, sent 50,000 troops to take advantage of the situation.
Confident that the main German forces were still in Bavaria and that only Mainz's 2,000 men had entered Austria, the Allies believed the intervention would succeed easily. Even adding Austria's 50,000 troops to Mainz's forces, the numbers were heavily against them—50,000 against 200,000. Britain, France, and their allies were certain victory would be theirs.
Meanwhile, Italy saw an opportunity as well. The Italian army, numbering 50,000, advanced through South Tyrol, hoping to secure Austrian territory while the Entente powers were occupied elsewhere.
From Mainz's perspective, the situation was clear: three enemy forces were converging on Austria:
1. The former Austro-Hungarian army, approximately 150,000 strong, composed of multiple ethnic groups.
2. Romania's army, 50,000 strong, still approaching.
3. The Italian army, 100,000 strong, moving through South Tyrol with the intent to outflank from the west.
"Our enemies total 300,000, while our forces number only 50,000," Mainz explained over the sand table, placing flags to mark each contingent. "Most of them are Austria's own troops. This battle will be extremely difficult. Any suggestions?"
Although the disparity in numbers was severe, Mainz had already devised a strategy. The enemy, despite their superior numbers, lacked coordination—giving the German-Austrian forces the opportunity to defeat them piecemeal.
"Colonel, how will the Austrian army enter the fight?" Moder, the regimental staff officer, asked.
"The Italian advance is predictable," Mainz replied confidently. "Once we determine their route, we will stop them before they can penetrate Austrian territory. The Alps will serve as our natural fortress—it's their greatest obstacle."
With determination and careful planning, Mainz prepared to confront three enemy forces simultaneously, confident that strategy, discipline, and surprise could turn the tide. The German-Austrian merger would not be derailed, even against overwhelming odds.