The point of including worldwide stock is to reduce risk in case the US has a recession, as not all other countries will be affected by that. The aim of the Bogleheads three-fund portfolio is to be reasonably balanced in terms of risk vs reward, which is why it includes bonds too. Past performance is not indicative of future performance, and in general it’s better to diversify (investing entirely in a single country isn’t really diversifying)
If you’re not risk-averse then 100% US stock is fine, just be prepared for larger drops than if it was more diversified.
The point of including worldwide stock is to reduce risk in case the US has a recession, as not all other countries will be affected by that. The aim of the Bogleheads three-fund portfolio is to be reasonably balanced in terms of risk vs reward, which is why it includes bonds too. Past performance is not indicative of future performance, and in general it’s better to diversify (investing entirely in a single country isn’t really diversifying)
If you’re not risk-averse then 100% US stock is fine, just be prepared for larger drops than if it was more diversified.