The only consistent determinant of long term returns has been valuation. The economy was great in the late nineties but it was a terrible time to invest because valuations were so high. By the same token the 1970's and The Great Depression were terrible economic times but great times to buy stocks.
The German DAX is trading at ten times earnings and a greater than 4% dividend yield. In the long run this is likely to be a great investment. Stocks don't trade at these types of valuations during good times. I am researching ways to invest in Germany. The only liquid large cap ETF I can find is EWG, which represents the MSCI Germany Index but is not very well diversified. If any readers know of anything better please let me know.