manwithdream, it really isn't very complicated. In a nutshell Daniel had a dream where he was told that "the word would go forth" (from Cyrus) to rebuild Jerusalem. This is repeated many times in the Tanach.

From the time the word went forth to rebuild Jerusalem the Jews had 70 shavuim in which to repent and avoid another exile.

Unfortunately the Jews didn't heed Daniel's dream. There was great divisiveness and as a result the final part of his vision (the destruction and next exile) would happen.

It is all very ancient history.
And everything that Sarah tells you, listen to her voice. Genesis, 21:12