Personally, I don't think its wise to bet solely on the US for future growth. We just invest in everything, VTWAX. One fund to rule them all.
Lots of debate on this and we will only know the answer in the rear view mirror.
Here is Dr. French's opinion on home country bias: https://famafrench.dimensional.com/v...home-bias.aspx
Here is a Vanguard paper on the subject: "Global equity investing:The benefits of diversification and sizing your allocation" https://www.vanguard.com/pdf/ISGGEB.pdf
Vanguard on International: https://investor.vanguard.com/invest...onal-investing
You may get an argument that something like 40% of the S&P's revenue is from outside the US, but that misses a lot of international markets. Companies like Volkswagen, Cemex, Shell, Nestlé, AmBev, ... and all investment opportunities in emerging markets especially China. Google "biggest companies in the world" and you will see how narrow a 100% home country bias is.
You may also get an argument (hello, @pb4!) that the international sector has underperformed in the last decade. To some that is a reason to avoid it, to some that is a reason to expect reversion to the mean, and to some it's a matter of principal to not pick sectors.
Re Buffet I love the guy, especially his pithy quotations, but an S&P focus excludes small and mid size companies, value companies, and many growth companies. I would at least make the "one fund" choice be a total US market fund.
So, recommendation? No recipe from me. Read and understand, then make your choice. Either choice will probably produce very attractive results.