United States doesn't run the world, especially musically, so that's the dumbest fucking thing you could post.
General rule is first release = release year.
I agree that the release year is the initial release rather than the US release. However, if we were to put together lists of the top bands by nation regardless of genre, we would need at least a top 200 for the US. Whereas, we would need only a top 20 or top 50 for most other nations.
Top 5 Nations (Population wise) of the World and how many metal bands per country (according to M-A):
1. China - 159
2. India - 112
3. United States - 17,257
4. Indonesia - 577
5. Brazil - 3,847
A couple notes...
1. The low numbers from other countries are probably from M-A being a primarily English speaking site.
2. Is music sung in English usually more popular than other languages? I want to say yes, but I don't know.
3. English is the most well-known language in the world so it makes sense that metal sung in English would be more popular. Just out of curiosity I looked up the status for the UK and they have 3,238 bands listed on M-A. Germany actually has more listed with 8,156, but Germany is pretty metal so...