Reddit reviews When God Took Sides: Religion and Identity in Irish History: Unfinished History

There are a lot of theories about this. Realistically speaking, religion and religious institutions are less important in the national and global age. There can be little talk of European religion without mentioning nationalism and statehood. Some good readings would include:

[When God took Sides: Religion and Identity in Irish History] (https://www.amazon.com/When-God-Took-Sides-Unfinished/dp/0199206937) by Marianne Elliot

[The Crosses of Auschwitz: Nationalism and Religion in Post-Communist Poland] (https://www.amazon.com/Crosses-Auschwitz-Nationalism-Religion-Post-Communist/dp/0226993043) by Geneviève Zubrzycki

[The Death of Christian Britain: Understanding Secularisation] (https://www.amazon.com/Death-Christian-Britain-Understanding-Secularisation/dp/0415471346) by Callum Brown

[Religion and the State in Russia and China: Suppression, Survival, and Revival] (https://www.amazon.com/Religion-State-Russia-China-Suppression/dp/1441112472) by Christopher Marsh

I would also include works from linguists like Benedict Anderson and Eric Hobsbawm, the works of politicians and leaders like Konrad Adenauer and Leon Trotsky, as well as apologists and critics like Fyodor Dostoevsky, C.S. Lewis, and Albert Camus.

If you are interested more in American religiousness, I haven't researched that much, but I would maybe point you to historical works on American immigration which include a lot of information on religious beliefs and institutions which provided communities and identities.

I recently read this which was an interesting take on the role of religion in Ireland.
https://www.amazon.co.uk/When-God-Took-Sides-Unfinished/dp/0199206937

It's an interesting read and gives what seemed to me at least a very accurate picture of the various religions in Ireland, the attitudes of their believers and how they got to the current mindset.

Worth a read if you have the cash, or get it in your library....