September 12 is also known as the ‘Day After’ – the first day after the World Trade center was attacked by terrorists, killing hundreds of civilians and changing the topography of Manhattan. The turn of the 21st century was welcomed ominously with violence. To commemorate this day, a museum was opened on this day 10 years after the event so that relatives of the victims could pay tribute to their loved ones. It was also on the 12th of September that Adolf Hitler joined the German Workers Party that later on went to become the Nazi Party. It changed the history of Germany and the world in the coming years. This day was important to Germany 50 years later, too, when the treaty was signed, unifying the country for the first time after the Second World War had torn it apart. Check out all the important events that happened on 12 September in human history.