The source provides an overview of the catastrophic failure of Napoleon's 1812 invasion of Russia, detailing how his massive Grande Armée of over 600,000 men was reduced to fewer than 50,000 survivors. While factors like the brutal winter and Russian scorched-earth tactics have long been blamed, the text emphasizes recent scientific breakthroughs, particularly DNA analysis of soldiers' remains found in a mass grave in Vilnius. This research, led by Nicolás Rascovan, reveals that the army was largely decimated by disease-causing microbes, specifically typhus and trench fever, both transmitted by body lice thriving in the unsanitary conditions. The essay asserts that this pathogen-fueled epidemic was a primary cause of the army's collapse, fundamentally reshaping the historical understanding of this decisive military disaster.