GWL = SPDR S&P World Ex-US
ITOT = iShares Core S&P Total U.S. Stock Market
SPY = You know what it is :-)
Taking 2008 market top as starting point, we see unison of movement in SPY , ITOT as well as GWL All three have same correction up until Aug 2013 (marked with vertical line) when SPY or US stock as a whole started to deviate from the world index (excluding US). As can be seen that the entire US equity market continues to propel forward with the same steepness in price movement. However, the same cannot be said about GWL anymore. GWL price movement has became less steeper. This differences might not be that noticeable after all.
Moving forward, the stark differences really became extremely noticeable when GWL started to go lower towards the channel bottom and ultimately broke the channel support in Aug 2014 and continue to move lower while SPY & ITOT continue to move higher
A round of applaud for SPY & ITOT and a thumbs down for GWL
Hence i can say that SPY & ITOT are really a class of it's own unaffected by world indices.
My biggest skepticism is this:
Does the market has to move in unison all the time? If this is so... the divergence between ( SPY & ITOT) with GWL would mean that sooner or later either GWL has to move up ( from Europe, JPY, China...etc) or SPY & ITOT have to move down for the market to be efficient overall??