The US policy in Afghanistan in the context of 9/11, under the broader rubric of the War on Terror (WoT), primarily was to topple the Taliban regime. Because the regime disagreed to comply with the US administration's demand to extradite Osama bin Laden, the alleged mastermind of the terrorist attack in the USA in 2001. However, the WoT project did not end with the collapse of the Taliban regime, but rather, it was transformed to a state-building project in Afghanistan. Why was the WoT project shifted to state-building, a project which has been in continuation for last 17 years? This article investigates the post-9/11 US policy in Afghanistan from the perspective of offensive realism. Particularly, it examines the causes behind the US policy shift in Afghanistan from the WoT to a state-building project and its continuity. The article argues that US state-building in Afghanistan has been driven by two major motivations: the first is to maximize security by securitizing itself from further terrorist attacks, and the second policy priority is to prevent other regional hegemons to emerge in South Asia. It further contends that through the Afghanistan policy, the US administration maintains an onshore balance against China and offshore balance against India.