Football is the most popular sport in the U.S. So naturally, the NFL has longed believed the sport would thrive internationally. In late 1980s, NFL officials bet on Europe. For the next 30 years, NFL Europe would try, fail, and try again, to conquer the hearts of European sports fans. Now, the sport of American football is giving it another go. So why hasn't the sport caught on? And will it work this time?