This is the fifth part in a series of eight exploring why the United States suffered no follow-up terror attacks after 9/11. To read the series introduction, click here. The 9/11 attacks led to a U.S. invasion of Afghanistan, whose Taliban regime was sheltering al-Qaida. That made sense. Then it led to a U.S. invasion of Iraq. That made no sense. The Bush administration claimed that Iraq's Saddam Hussein had close ties to al-Qaida.