Within the span of seven months in the midst of the Great War, Albert Einstein published two seminal papers, on "Quantum Emission and Absorption" and "Field Equations of Gravitation", that laid the foundations of modern physics. Our century-long odyssey starts here, taking us through the rise of holography, fuzzballs, firewalls, quantum chaos, and gravitational wave astronomy. However, in the end, it will land us back within those fateful seven months, where Einstein's July 1916 ``Strahlungs-Emission und -Absorption nach der Quantentheorie'' may prove to be the ultimate undoing of his December 1915 ``Die Feldgleichungen der Gravitation''. I will lay down the theoretical and observational arguments on both sides of (the latest battle) in Einstein's Great War.