Originally, there was no division between 1 and 2 Chronicles. But in about the third century B.C., a division was made by the translators of the Septuagint version of Scripture.
There's a good possibility that 1 and 2 Chronicles was written (or compiled) by Ezra, the famous Jewish reformer and scribe, about 400 B.C.
First Chronicles concentrates on the history of David's reign. At first glance, it seems to repeat what we find written about David in 2 Samuel. But closer inspection reveals many things that were not recorded there.
Second Chronicles deals mostly with events during the reign of Solomon and the kings of Judah. The final chapter tells of the deportation of the people of Judah to Babylon and the edict of Cyrus, many decades later, that gave them permission to return to their homeland.
The message that stands out most prominently in the Chronicles is this: disobedience to God brings suffering and disappointment. Obedience brings divine blessing.