AS FAR AS the differences, THE TWENTIETH CENTURY did a straight forward newsreel type of presentation; although the events depicted and reported on were far from being news. A typical half hour might cover Pearl Harbor, Woodrow Wilson, Poet Robert Frost or the 1919 Black Sox Scandal.
WE RECALL THAT it was always interesting, well done using excellent archival news film and kept us entertained; which of course is a very important element. (Can you say 'Nielsens?")
OUR GUESS IS that CBS slotted this in place of YOU ARE THERE, which was probably running out of 'THERES' and starting to slip in the ratings. It also could be their answer to the very popular Historical Documentary on NBC, VICTORY AT SEA.
THAT'S JUST OUR guess!