The Boundary War is conflict in the backstory of AMAIM Warrior at the Borderline.
Japan was on the brink of destruction during the mid-21st century. Failed economic policies, the aging population combined with low birthrate. Problem after problem pushed Japan to the verge of collapse. To help, powerful countries and allied powers stepped in. In the name of economic aid, medical support, and peacekeeping, each nation deployed a vast number of people, slowly expanding their territory, until finally, an armed conflict arose. Later, this battle was called the Boundary War. The nations deployed humanoid war machines called AMAIM. Unmanned AMAIMs with tactical AIs became the main players on the battlefield, engaging in battles all over Japan. Japan was virtually divided up and ruled, and its people fell under outside control.