A year ago, most Americans were largely unfamiliar with the group now known as ISIS - Islamic State of Iraq and Syria. This summer, ISIS has become a notorious name, and was called a "cancer" and a "network of death" by President Obama.
Now, the U.S. is at war with ISIS and conducting airstrikes in Iraq and Syria. How did we get here?
NBC News Foreign Correspondent Ayman Mohyeldin answered reader questions about ISIS, and how we got here, in a live Twitter chat on Tuesday.
Read on for a recap of the questions and his answers.