U.S. sales of VW's Tiguan SUV, which competes with the Ford Escape and Honda's CR-V, were down over 20% last month. Photo credit: VW.

It's a story that many Americans have missed, but German auto giant Volkswagen (OTC:VWAGY) has been on a massive global growth push in recent years. VW executives have made no secret of their goal: To surpass General Motors (NYSE:GM) and Toyota (NYSE:TM) and become the world's largest-selling automaker by 2018.

The growth of VW's Audi brand has helped the company gain huge profits, and VW's success in China has greatly boosted its global sales totals. But lately, the VW brand itself has been struggling: Global sales were actually down last month, even as nearly all of VW's key competitors posted increases.

What's the deal? In this video, Fool contributor John Rosevear dives into the latest numbers from Volkswagen -- and looks at some surprising declines that may spell trouble for the VW's world domination plans.