Final answer:
The disastrous outcomes of the 1812 Russian campaign were due to a lack of trained troops, Russian scorched-earth tactics, harsh winter conditions, supply issues, and debilitating diseases. These factors caused massive casualties and greatly weakened Napoleon's army, leading to the end of his empire.
Step-by-step explanation:
France's 1812 Russian campaign marked the beginning of the end of Napoleon’s empire for several reasons. Napoleon’s forces were comprised heavily of new recruits and soldiers from non-French territories, many without sufficient military training, which weakened the coherence and fighting capability of his army. This logistical weakness was compounded by a scorched-earth strategy employed by the Russians, who retreated while destroying or taking with them anything that could be used by the French troops, resulting in shortages of food and supplies. The Russians avoided large-scale engagements preferring guerrilla tactics, which, combined with the onset of the harsh winter, further devastated Napoleon's army. Disease and desertion were rampant, and the scorched-earth policy also meant that Napoleon’s army could not live off the land. Ultimately, of the 650,000 soldiers who began the campaign, only about 100,000 survived the retreat from Russia, a blow which severely weakened Napoleon's military might and exposed his vulnerability, prompting his former allies to turn against him. The catastrophic losses and dwindling support led to the eventual downfall of his empire following further defeats and his abdication in 1814.