The U.S. equity market accounts for just over half of the global equity market capitalization. Developed markets outside of the US, emerging and frontier markets account for 46% of the world market capitalization. So investing in just US equities will not capture the potential growth of these markets according to an article by Wes Crill at S&P Global.

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Source: Why Should You Diversify, S&P Global

I agree with Wes. US equity investors must diversify globally. Simply going with US multinationals to capture the growth of foreign markets does not work in all scenarios.