Islamic State (I.S.) militants have been advancing across large parts of Iraq and Syria killing thousands of believers.
Barack Obama has authorised air strikes in Syria for the first time as well as an expansion of strikes in Iraq.
During a televised address to the American people Mr Obama also confirmed he was sending almost 500 more US troops to Iraq to assist the country's besieged security forces.
"This is not our fight alone," the president warned.
"American power can make a decisive difference, but we cannot do for Iraqis what they must do for themselves, nor can we take the place of Arab partners in securing their region
"Our objective is clear: We will degrade and ultimately destroy Isil [IS] through a comprehensive and sustained counter-terrorism strategy," he added.
But the president did continue to rule out putting U.S. troops on the ground in Iraq.
In recent weeks America has been urging its allies in Europe and the Middle East to help in the fight against Islamic State.
France has confirmed it will take part in air strikes is needed, Germany's said it will send weapons to Kurdish forces whilst the UK has also agreed to send arms.