How did certain bands end up assigned to specific services anyway?

The short version is that the hams got the leftovers, and then the leftovers turned out to be the best part. In the 1910s shortwave was considered worthless. The commercial and government interests of the day wanted the longwave spectrum becasue that's where the reliable, well-understood propagation was. Amateurs got pushed up into what everyone assumed was useless territory above 200 meters, more or less as a containment zone. Then the transatlantic test hearings in the early 20s happened, hams proved shortwave coud cross oceans with a few watts, and suddenly that 'worthless' spectrum was the most valuable real estate going. The 1927 Washington conference is where alot of the modern band structure got formalized, and hams had earned enugh goodwill and military utility by then to keep a few slices. everthing since has been incremental treaty work at ITU world conferences, wich is why the edges look so arbitrary. Allocation tables are basicly sediment, layers of decisions made with the technology and politics of the moment, never cleaned up afterward.

For reading material, old QST issues are honestly the best source I've found. The ARRL has the archives online free and reading issues from the 20s and 30s is wild. You can watch them argue about moving from spark to CW, fight over phone privileges, and gripe about the exact band edge squabbles you're asking about, all in real time. Also look up anything by DeSoto, he was in the middle of alot of it. When I studied for my General I kept a notebook of this stuff becuase it made the allocation table acutally stick. Knowing why 20 meters is shaped like it is beats memorizing it.

Wild that they got shoved into the junk frequencies and it turned out to be the good stuff. Makes me wonder if the same trick coud happen again, like is there some band today that all the big companies are ignoring that could suddenly matter? I only know enought to pass the practice tests so this history stuff is all new to me, but it explains why the little gaps between big services always seemed so random when I was looking at the charts.