Iraq- Should America be the police of the World?

During the United States' eight-year presence in Iraq, American forces acted as a buffer between the two Islamic sects, albeit with limited success. But U.S. forces fully withdrew at the end of 2011 when Washington and Baghdad could not reach an agreement to extend the American military presence there. As of June 16, 2014 we are sending 275 troops to protect Americans in Iraq. While the country is being assaulted byt he al-Qaida inspired group Islamic State of Iraq. They quickly took control of key Iraqi cities last week. I think as soon as the first soldier get killed we will be all the way back  in action . Why don't they send soldiers to protect us Americans in Detroit we're dying here every day.