Final answer:
The duty mentioned by Osama bin Laden to kill Americans relates to his leadership of Al Qaeda and their actions, including the 9/11 attacks, which led to the US declaring war on terrorism and the invasion of Afghanistan.
Step-by-step explanation:
The question pertains to statements made by Osama bin Laden regarding it being the duty of Islamists to kill Americans. These statements can be linked to the broader context of Al Qaeda's terrorist activities and bin Laden's views on the West, which he saw as a corrupting influence on Islam. Osama bin Laden was the leader of Al Qaeda, which carried out the September 11, 2001 attacks in the United States, actions that were meant to be a statement against American policies and presence in the Middle East. Following these attacks, President George W. Bush declared war on terrorism and demanded that the Taliban turn bin Laden over or face attack from the United States, leading to the invasion of Afghanistan in October 2001 and the eventual killing of bin Laden by US Navy Seals in May 2011.