https://en.wikipedia.org/wiki/Collation#Radical-and-stroke_s...

https://en.wikipedia.org/wiki/Kangxi_radicals

https://en.wikipedia.org/wiki/Kangxi_Dictionary

https://en.wikipedia.org/wiki/Zihui

https://en.wikipedia.org/wiki/List_of_Shuowen_Jiezi_radicals

The alphabet is a marvelous invention. I seem to remember that Europeans in China (and places with a large Chinese diaspora) used alphabetical sorting of whatever romanization they favoured (different between English, French, Dutch). Much easier than radicals and stroke counting.