dobriennm wrote:The Author has to make a bridge book. To do otherwise would be like writing a series that starts in 1910 with a book stopping at the end of World War I and then starting the next book with the German invasion of Poland and depending on flashbacks to go over the twenty years between World War I and II, covering the Versailles Treaty, The Russian Revolution, formation of the USSR, the Great Depression, Hitler's rise, Japan turning from ally to enemy, etc.
Flashbacks would only be needed for those things the author deems important. There are over 70 years between The Hobbit (TA 2941) and the main plot of The Lord of the Rings (TA 3018-19), yet I don't think the story suffers for lack of a book bridging the two.