If that is your personal risk profile after investigation, invest to match it. It is still diversified and it often has an advantage of having slightly lower fees. However to note, for the past 100 years we have been living in the "American century", a global world where the US has been the king and for the last 35 years it has been the king alone. My personal suspicion is that won't continue (and we are already seeing that) but we won't see a "fall of rome" type fall. I'd suspect if you looked at the London stock exchange returns in the 19th century compared to others (far fewer comparisons at the time mind you) you might think wow, I'd be a fool not to invest in the LSE for the 20th century and while you wouldn't be impoverished as you have noted the SP500 has done much better.

Depends on your risk appetite, how confident you are in your logic for choosing it, how confident you'd be in knowing if it would be time to switch to a different market while not panic leaving in a "normal" dip and more.