https://celticlifeintl.com/history-of-celtic-music/

An overview of Celtic music from different cultures and how it has evolved over time.

https://fiveable.me/music-of-the-modern-era/unit-8/celtic-music-influences/study-guide/QRFfxqldD8asavgh

Listings of different characteristics of Celtic music, including instruments and vocal styles, and how those are heard in modern music.

https://londoncelticpunks.wordpress.com/2016/02/28/how-the-irish-and-the-scots-influenced-american-music/

A breakdown of techniques and styles from Celtic music that have translated into American country music.