The scope of this question surpasses my ability to answer in a a Reddit thread, as chess has evolved over 1500 years in dozens of locations. I've answered some snippets of these questions over the years, and will link to them instead.

Here I answer how castling and en passant developed.

Here I write about how rules became standardized over time.

Here I write about how chess strategy has changed over time.

If you have specific questions regarding a certain rule, time period, etc., feel free to post it and I'll try to answer!