Norden Incident

The Norden Incident was a battle between the Imperial Northern Army Group and the Legadonia Entente Alliance Army. It is widely considered the start of the World War.

Background
A long time ago, the Empire and Legadonia Entente Alliance had an unofficial dispute over the drawing of the national border. Legadonia used to claim the territory of Norden, which was under the Empire's control, but the Treaty of Londinium, which was mediated by the United Kingdom, allowed the Empire and Legadonia to resolve their national border dispute by compromising and recognizing a common national boundary. Since it was officially named a provisional demilitarized zone, and was confirmed by the executive government of both nations as a de facto national border, in the international politics arena, there's nominally no dispute over this territory. However, multiple isolated accidents have occurred along the border recently. There has been unintentional fire on both sides, which led to firefights due to misunderstanding, causing the situation to become tense.

Legadonia Entente Alliance
The Legadonia was facing the sluggish economy, the widening wealth inequality, and the unemployment rate that refused to fall. Those finally led to the change of Legadonia’s policies. Due to the change in political regime and the installation of new leaders, the rise of nationalism demanded a huge shift in national policies. Since the Empire had territorial disputes to most neighboring nations, which formed an alliance against the Empire, the Legadonia's government expected the Empire would make some degree of concession. Once again, Legadonia claimed the territory of Norden as a sort of domestic propaganda. Some government spokesperson even described this military operation as a “highly organized hiking exercise under pressure”. Later, they issued an ultimatum.

“Imperial soldiers are to withdraw from our nation's territory within twenty-four hours.”

The Empire
The high command ignored the turbulent situation and judged it to be merely brinkmanship diplomacy, expecting the neighboring nations such as Republic and United Kingdom would probably fear that their past efforts to help them would be lost, and would stop their military operations. The Empire had strong military strength that even during peacetime, a corps-sized garrison was deployed to the border under the pretext of routine patrolling. After Legadonia issued the ultimatum, they followed the plans laid out by their country, mobilizing the cautious bureaucracy and military arm in preparations for the theoretical attack that might happen theoretically. In preparation for war, an additional corps was formed on top of that by mobilizing troops that weren’t part of the garrisoned forces. They gathered large amounts of resources and mobilized units, and even invited presses from other countries and permitted them to stay in Norden.

Invasion
One day in June, 1923, Entente Alliance sent the Imperial Army an advisory to the Imperial army in Norden.

“Disarm and surrender to the advancing Entente Alliance Army or leave immediately.”

Subsequently, the Entente Alliance forces were crossing over at multiple locations. As the response, the Empire declared war on Legadonia Entente Alliance. The Imperial artillery bombarded the Entente Alliance Army by air bursts and time on target missions, and Imperial armored forces and other troops rapidly deployed on the front. The Imperial air forces built an air defense network that was properly set up, with air units and mages ready to intercept. Later, the Entente Alliance invading forces had been destroyed. Besides, when the Empire was about to switch to the offensive and pursue the enemy forces, a Legadonia aerial mage company broke through the Empire's air defense line, and attacked an Imperial mage observer. The Imperial mage observer got heavily injured yet successfully kept them from attacking the Imperial artillery position. This mage observer sooner was awarded the Silver Wings Assault Medal for her excellent performance.

Aftermath
Although the Empire had already defeated the invading forces, meeting their national defense objectives, the General Staff decided to mobilize the entire Great Army, launching a major offensive against Legadonia. The Imperial General Staff attempted to finish off the Entente Alliance once and for all, and overrated the flexibility of Great Army. This decision finally led to a series of wars that are known as “The Great War” in future.

Reference
Deus lo vult - Chapter I The Sky In Norden.