Complex sentence: The first entry (released on Thanksgiving Day 1948), covering the crisis/war years 1933-1945, was a groundbreaker in that it used actual clips of radio news coverage and speeches of the major events during that 12-year time span.
Split into simpler sentences: The first entry in the series, released on Thanksgiving Day 1948, covered the crisis/war years 1933-1945. It was a groundbreaker in that it used actual clips of radio news coverage and speeches of the major events during that 12-year time span.