What was the most significant international event that affected the US in 2021?

The most significant international event that affected the US in 2021 was the Taliban takeover of Afghanistan, which began in August and concluded in September. The US had been involved in the conflict in Afghanistan since 2001, and the withdrawal of US troops under the Biden administration was a highly controversial move.

The Taliban's rapid advances across the country caught many by surprise, and the Afghan government collapsed quickly in the face of their onslaught. The chaotic scenes at the Kabul airport as Afghans and Americans tried to evacuate added to the drama and tension surrounding the event.

The fall of Afghanistan to the Taliban has far-reaching implications for the region and beyond, including potential impacts on US foreign policy, relations with other nations, and the global fight against terrorism. It also sparked debates and criticism within the US regarding the handling of the withdrawal and the fate of Afghan refugees and allies.