20 years since the 9/11 horror, the deadliest attack on US Soil

The entire world was shocked when Al-Qaeda terrorists smashed two planes into New York's World Trade Center, killing approximately 2,753 people. A third commercial jet hit the Pentagon, killing 184, and 40 more died after a fourth plane crashed into a field in Shanksville, Pennsylvania after a passenger revolt. It was the first foreign attack on the US mainland in nearly two centuries.