Near the top of my reading list for the last few years (i have a long list) is Lyall's "Divided Armies", in large part because of the innovative procedure he used to select his comparison case studies.

The thesis of the book—as i understand it, one of the few on the subject grounded in evidence—is that ethnic inequality in a military, through several mechanisms, lessens its effectiveness.

https://press.princeton.edu/books/paperback/9780691192444/divided-armies

Divided Armies

The open question here is not whether reactionaries want meritocratic advancement (they don't); it's whether they want a weak military.

The case that they don't is easy: They want to expand and conquer, and they keep acting in ways that weaken it because they're delusional. But i lean toward a case that they do: Fragmentation of our (comparatively) legitimate military would make it easier for their loyalists (both military and militia) to seize power domestically.

https://www.npr.org/2026/03/27/nx-s1-5763863/hegseth-soldiers-promotions