Obama said other nations are behind America's "mission." What "mission" is that exactly?

I just watched Obama's speech on CNN.com. Obama said that unlike Vietnam, many nations are behind the U.S. in this war because they support our "mission." What is our "mission" exactly? Bush said it was to find WMD (weapons of m destruction) then later he said it was to take out Saddam Hussein. What is the U.S.'s new "mission" under the Obama administration?