Why did the Roman Catholic and Eastern Orthodox churches split in 1054? Were the theological differences really irreconcilable? Or did the split come about for economical or political reasons? Or did Leo IX and Michael Cerularius just hate each other? Why did this schism stick when earlier disagreements (Like the Photian Schism in 863 CE) were able to be reconciled?
One of the best works on the subject is, ironically, a book that does not intend to tell the story of the separation but instead provide a balanced history of the Eastern and Western (and Syrian) churches in the 7th to 11th centuries. Indeed, it argues that the schism was not considered so significant at the time as we regard it today (much like some scholars have argued re: the fourth century Creed of Nicaea...)
The book is: Andrew Louth, Greek East and Latin West: The Church, AD 681–1071.
If you have the time and interest - and want a nuanced account of what was going on at the time, I highly recommend it.