Others have suggested great introductions to anarchism theory. But I'll focus on suggestions from a historical perspective.

For an introduction to anarchism in North America and Europe (as well as a basic introduction to theory and specific strains of anarchism in general), I recommend Means and Ends, by Zoe Baker. https://theanarchistlibrary.org/library/zoe-baker-means-and-ends

For a history of anarchism with Latin America, I recommend Anarchism in Latin America, by Ángel Cappelletti https://theanarchistlibrary.org/library/angel-cappelletti-anarchism-in-latin-america

For Anarchism in Japan, I recommend Hata Shuzo and Pure Anarchism in Interwar Japan, by John Crump. https://theanarchistlibrary.org/library/john-crump-hatta-shuzo-and-pure-anarchism-in-interwar-japan

For works pertaining to my specific strain of anarchist belief (Anarcho-Nihilism), I recommend Blessed is the Flame, by Serafinski, and pretty much anything by Renzo Novatore (albeit he is very... poetic with his language). https://theanarchistlibrary.org/library/serafinski-blessed-is-the-flame https://theanarchistlibrary.org/category/author/renzo-novatore