Final answer:
Typhus was the disease that severely affected Napoleon's troops during their invasion of Russia, compounding their suffering from other strategic and environmental difficulties.
Step-by-step explanation:
The disease that did a lot of damage to Napoleon's French troops during the invasion of Russia was typhus. While the French army was suffering from multiple hardships such as the harsh winter, scarce supplies, and the Russian scorched earth policy, typhus, exacerbated by malnutrition and the cold, swept through the ranks and significantly reduced their numbers. Diseases like smallpox also played a horrendous role in historical conflicts, particularly affecting Native Americans who had no immunity to such European diseases, leading to catastrophic losses.