My thoughts on portfolio diversification with international stocks and etfs

Past few days, I was thinking about how to modify my existing portfolio for a possible downturn in US stock market. In my retirement (401K and Roth IRA) and personal brokerage, about 90% holdings are on US Stock and ETFs. My portfolio is very much on domestic equities and luckily, I ripped benefits from the roaring US equity market in last several years. Same may not be true for our fellow investor friends on other side of the pond or in Asia/Latin Americas. While our benchmark S&P 500 index returned over 180% since 2010, rest of the world index returned mere 15-20%. I hope in 2020, US stock market will keep roaring but analyzing the historical trends invoking some new thoughts. Recently I came across a very concise article on this from Fidelity Investment and here I am trying to summarize it. Apparently, there is cyclical turn between US vs International marke...