Scott Grannis points out how important trade is to your portfolio's bottom line (NIPA is "a measure of profits based on information supplied to the IRS"):
Since the end of 2001, NIPA profits have almost doubled (+185%), while nominal GDP has increased by only 80%.
Over the years I've argued that this is at least in part due to globalization. Large and successful US corporations have been able to generate a much higher level of profits by selling into the rapidly expanding global market. Global GDP has increased 125% since 2001.