A friend in Cyprus recommended the book American Indian by the late R J Rushdoony recently on Goodreads and I was able to pick up a kindle version very cheaply (see here). It is a collection of 20 slightly overlapping essays on the subject from various times. if you grew up in the sixties like me, playing cowboy and Indians and watching old westerns on TV then you will already be interested in the subject. Rushdoony lays some myths to rest and writes sympathetically towards the native American and deprecatingly of most US government attempts to "solve the problem". Some of his assertions may sound controversial if you are not a aware of or sympathetic too the wider work of his Chalcedon Foundation. The essays are well written and a well thought out and will repay reading to any thinking Christian, whether the needs of native Americans are high on your agenda of interests or not. It would be good to hear that other Rushdoony materials currently hidden away in old magazines are being given similar treatment. The editorial work on this volume is of a high standard. PS If you're worried not a trace of theonomy or even post-millennialism in these pages.
Bonhoeffer uses a similar phrase 'worldly Christianity'. It's J Gresham Machen that I want to line up most closely with. See his Christianity and culture here. Having done commentaries on Proverbs (Heavenly Wisdom) and Song of Songs (Heavenly Love), a matching title for Ecclesiastes would be Heavenly Worldliness. For my stance on worldliness, see 3 posts here.