Why did Barrack Obama win a Nobel Peace prize?

It was a nudge in his direction to keep him in line and on agenda for the duration of his presidency. He didn't win for anything he's done, but what the Prize Committee hopes he'll do. The Prize Committee has notoriously endorsed people who support globalization and social democracy. They knew that by awarding Obama the prize that he would be held to a certain standard and be expected to tow the line or risk losing face by not following through on promises.