"We are uniting the world against a unified threat, and the president's strategy will succeed because doing it with allies and partners isn't just smart, it's strong," US Secretary of State John Kerry said of the president's speech.
Kerry was in Baghdad on Wednesday, lauding the creation of a new, inclusive government that could take on the security challenge of Islamic State.
The secretary will also travel to Amman, Jordan and Jeddah, Saudi Arabia to rally support for the fight this week. US officials say the Saudis are prepared to "fully cooperate" with the US on training moderate Syrian rebels to help combat the group.
"Defeating this common enemy calls for a common cause, and we're taking it on to succeed together," Kerry continued.