it's a good doomsday

Notes for the below: There are several canonical nations in the ME universe that are combinations of modern-day nations:

United North American States (UNAS): USA, Mexico, Canada

European Union (EU): As today; I have used the current listing of nations, though presumably some things may have changed by the 2100s. Member nations are not specified in canon AFAIK.

Chinese People's Federation: Nations are undefined in canon and there is no real-world equivalent, so I have left China as a standalone nation.

There is a pretty simple interpretation of "largest nation" and that is by population. The most distant population projections I could find were estimates for 2100. Here is the list, from largest to smallest:

(Yes, you are getting my finest excel.) (Note: This data is from roughly 2016 when I did the original research.)

Nice and straightforward, right?

But, power was also presumably involved here, and so there is a second way to define largest: by economy.

(I did update this data, as the impact of clean energy has radically changed some predictions since 2016.)

Unfortunately, predictions that encompass a large enough number of countries for this exercise only go out to 2050, which is a full hundred years shy of our goal. But there are some interesting trends, namely several nations not often included in modern-day economic discussions gaining considerable influence.

So, how do we combine these lists? First, obviously, look to see which nations appear on both. That nets us 11 out of 18, not bad.

The remainder are a judgement call. I chose to slightly favor population, and look for nations with large predicted populations that were also relatively high on the economic list.

Here's what I got, in alphabetical order:

Nations in YELLOW appeared in the top 18 by both projected population and GDP. Nations in ORANGE (italics) were my best guesses for the remaining seven nations, bringing us to 18 signatories.

Finally, I should probably note that while this list contains no headcanon, for my own purposes, I did define the CPF as well as a few other non-canonical nation conglomerates, since that seems to be a trend in Mass Effect. World events in canon or headcanon would also substantially influence this list in ways too numerous to discuss, but are also something I would encourage anyone interested in this data to consider.

Why is this important? Because while I assume people living in the Alliance are not solely from these nations, they have presumably defined the laws, culture, and priorities of the Systems Alliance for the past ~40 years, and likely will continue to dominate going forward. While obviously I cannot predict how these nations may evolve, in the real world, they represent a wide array of legal and political systems, cultures, and philosophies on matters important to your average Alliance citizen, who is living in some mélange of these ideas, good and bad, on a daily basis.

TLDR: Mass Effect should be a lot less white, a lot less Canadian American UNASian, and considerably more religiously diverse.