What is the Islamic State of Iraq and Syria's relationship to al-Qaida?
ISIS was once considered an affiliate of al-Qaida, but the two groups have broken over ISIS's role in Syria. Al-Qaida has criticized ISIS for being too brutal and has complained that ISIS's zeal to establish an Islamic state has distracted from the current push to topple Syrian President Bashar Assad.
Which is more powerful, al-Qaida or ISIS?
There is no simple answer to that question, but ISIS's recent military victories and its control of a swath of land larger than many countries in the Middle East suggest that its military power, if not its influence, now exceeds al-Qaida's. It has fielded a conventional army that has bested the Iraqi military and has resisted assaults in Syria by al-Qaida's affiliate there, the Nusra Front.
What is the United States' stake in ISIS's advance?
The United States first clashed with ISIS in 2004 in Iraq when the group was known as al-Qaida in Iraq. Over the ensuing years, the group killed hundreds of American service members and attacked embassies. It continues to issue threats against the United States and the West. The establishment of a radical Islamist state in the areas ISIS claims would allow terrorists to organize only a short distance from Israel and Europe.
Los Angeles Times