It's a milestone we haven't seen in a long time... 20 years, to be exact. For the first time in two decades, General Motors (NYSE:GM), Ford (NYSE:F) and Chrysler all gained market share in the U.S. in the first half of 2013.

It's proof that the Detroit renaissance is for real, but can the Big Three keep it up? In this video, Fool.com contributor John Rosevear looks at what's driving the American auto sales boom and ponders why Detroit's winning streak may be at risk.