Groceries aren't a single national market, and its quite likely that such a merger would both create both monopolies and monopsonies.

Its also quite likely that the big grocery merger won't happen as planned for that reason.

Albertsons + Kroger is like 90% of the market in Seattle, where I live, though.

It's very location-dependent. In my midwest metro I believe they'd be less than 5% of the market. I'm sure Albertsons and Kroger each have local monopolies in different regions.

I think they have a good point, though. I would like the laws to prevent a single corporation from being 90% of all groceries for an entire state even if they aren't anything close to a monopoly from a national perspective.

That doesn't seem likely. According to this source, Frey Meyer (18.4%) + Safeway (17.3%) would be the clear market leader with over 35%, but there's still robust competition from Costco, Walmart, and others.

https://www.axios.com/local/seattle/2023/04/24/seattle-favor...

Note that Fred Meyer (18.4) and QFC (14.1) are already both owned by Kroger. So that would be 49.8% post-merger, per those figures.

These figures seem to be for the Seattle metro rather than the city itself. Costco might be a competitor in some sense but it doesn't serve the area I live -- the nearest one is a 45 minute drive away. WinCos are even further away -- they serve some of the suburbs, but not the city of Seattle. Ditto Walmart. I've never heard of or seen Campeon. Whole Foods / PCC exist, but are expensive. Trader Joe's is fine but not really a full grocery store.

With the remainder being made up of Trader Joe's and ...

... Amazon

Yeah although TJ's is like 6% of the marketshare of the big two (and Whole Foods / Amazon is ~5%) (see sibling comments).