Complex sentence: Deemed by some to be his "magnum opus," the book was published in two volumes, the book was readied for the press in the spring of 1952 with the first volume appearing in August 1952 and the second volume published posthumously in May 1955.
Split into simpler sentences: Deemed by some to be his "magnum opus," the book was published in two volumes, with the book readied for the press in the spring of 1952. The first volume appeared in August 1952 with the second volume published posthumously in May 1955.