The United States marks the 25th anniversary of the September 11 attacks.

Speaking to DW, Peter Hahn, Professor of History at the Ohio State University, explains the anniversary’s place in collective US memory, also looking back at key events that followed in the wake of the attacks.

"9/11," Hahn says, "and especially the decisions made following 9/11, namely the decisions to invade Iraq and to wage global war on terror, those might have accentuated or accelerated what would have been a normal slower American decline from that unique circumstance of the post-World War II / Cold War position it had gained."