What led to the division of Ezra-Nehemiah?

Question

Modern consensus is that the books of Ezra and Nehemiah actually comprise a single work which was subsequently divided into two. How is it that scholars realized this was the same book (Does it have anything to do with 1 Esdras?) and why is it that the book was split in half in the first place?

The Anchor Yale Commentary, for example, is simply called "Ezra-Nehemiah" and the preface begins:

The period and literary deposit of Ezra-Nehemiah pose for the student of the Old Testament some of the most difficult and tantalizing problems connected with biblical history and literature

This is also true of Hermenia, and many other commentaries I hold. I also remember studying these books as a single work in seminary, but I forget the what led everybody to the conclusion it was one book.

The Ayc in commenting says:

The confusion of the materials in these books is abundantly clear to any observant reader in our present arrangement. Earlier students of the Bible recognized it: they tried to rearrange the various episodes into what appeared to them to be the proper order. Probably the first serious attempt to do so was made by the compiler of I Esdras, whose main interest seems to have been in the law—for he begins his work with the Josian reformation and concludes with Ezra’s reading of the law.

Answer 1

According to Dr. Constantinou many of the books were separated when they were translated into Greek because the addition of vowels made individual scrolls too ponderous. Since Bibles in English tend to follow the Septuagint order even though they follow the Masoretic texts, they remain split.

I went back and found the place where she discusses this: here. She discusses this from about minute 23:40-26:00. Please note that she does not specifically mention Ezra/Nehemiah.