I was surprised I couldn't find a graph like this already on the forum, so I made one and thought I would share it:
The data is from the 2022 EA survey,[1] and here is my sheet.
The main surprising thing to me is that English-speaking countries are less dominant than I expected, in this per capita framing. My vague sense was that the EA community was notably more popular in the Anglosphere than even in other rich countries, but eyeballing this data makes me think I was wrong: Northern/Western Europe seems to have quite comparable rates of EAs.
And what on earth is happening in Estonia? Perhaps some Estonian EAs can tell us all what you are doing that works so well!
- ^
Maybe there are quite different response rates by country, and this could explain some of the variance but I assume there isn't a large or systematic effect here.

Yeah, given the GDP-per-capita graph shared by William the Kiwi, and Estonia being the home of one of EA's most generous donors, I suspect that availability of philanthropic funds may be the bottleneck for local EA growth.
It wouldn't surprise me if low-GDP countries have many stories like this one or this one, of motivated people struggling to obtain funding due to lack of connections with philanthropists. If true, that would be an unfortunate situation -- lower GDP per capita often goes with a lower cost of living, meaning you get more bang for your philanthropic buck, all else equal.
Maybe we need a new sort of "digital nomad EtG/grantmaker EA" who travels around, networking with EAs in the developing world to identify great giving opportunities. This could go well with a cause area like AI alignment which can be done anywhere and could benefit from fresh thinking:
https://forum.effectivealtruism.org/posts/eToqPAyB4GxDBrrrf/key-takeaways-from-our-ea-and-alignment-research-surveys