Aegis War

The Aegis War is a cataclysmic war in Xenoblade Chronicles 2. The war involves both Aegises: Malos and Mythra. It is the main focus of Torna ~ The Golden Country and its legacy plays a role in Xenoblade Chronicles 2.

Cause
The initial spark is when Amalthus brought back two Core Crystals; Malos and Mythra's to Alrest after climbing the World Tree. Back in Indol, he awakens Malos who then lost control of him and proceeds to raise the entire world with his destructive powers. To contest him, Amalthus gave Mythra's Core Crystal to Addam who she awakens as his Driver at Olethro Ruins.

Torna ~ The Golden Country
During the Aegis War, at least two Titans sank into the Cloud Sea, Coeia being among them to Malos's rampage. At one point, Malos returns to Amalthus to taunt him and reveals that the Kingdom of Torna is his next target.

Legacy
Although Malos was defeated and the war ended, it left a huge impact on Alrest; people began to fear the power of the Aegises. Some nations desire that power while others want to destroy it. Amalthus then bars entry to the World Tree due to the war, and enlisted Ophion to guard it from any intruders. Jin and Malos forms the Torna organization with intention of obtaining the Aegis to open the way to the World Tree to kill the Architect and destroy Alrest due to the role the war played in the death of Lora.