Lego became the world's largest toy company in 2014, overtaking Mattel (MAT). But the Danish company broke the news to fans this week that it may not be able to keep up with demand during the holiday season. Lego popularity has been steadily on the rise following the success of 'The Lego Movie' and licensing deals for 'Star Wars' and 'The Avengers' building sets. The plastic brick maker saw sales increase 18 percent in the first half of the year, a higher than expected demand. Only Europe will be hit by the shortage as the U.S. market remains well stocked. Holiday demand for Lego doesn't seem to be reflected in the rest of the U.S. retail sector, as analysts predict slowing growth in holiday sales this year.