Americans are commemorating one of the deadliest terrorist attacks on the country's soil.
Nearly 3,000 people were killed when hijacked planes rammed into the trade centre, the Pentagon and a field near Shanksville on 11 September 2001.
Ray White speaks to US foreign policy expert Brooks Spector about the impact of 9/11.
Here we are two decades later, the possibilities of non-state terror remain with us.— Brooks Spector, US Foreign Policy Expert
The situation in Iran remains unstable. The situation in Syria, it is a country that has taken a devastating body blow to its physical infrastructure and in the population. You have to say that the 'war on terror' has not ceased and it probably won't.— Brooks Spector, US Foreign Policy Expert
We are at the point in the world where the knowledge about the creation of nuclear weapons and dirty bombs is so widely disrupted around the world.— Brooks Spector, US Foreign Policy Expert
Listen to the full interview below...