What was the deadliest pandemic in human history?

The answer

The Black Death (1347–1353) killed an estimated 75 to 200 million people across Eurasia and North Africa, wiping out roughly 30–60% of Europe's population. The mass die-off led to abandoned farmland being reclaimed by forests, absorbing enough CO₂ to cause a measurable drop in global temperatures. It also upended feudalism, as surviving workers could demand better wages in the resulting labor shortage.