Was the war started because of the Illegal books? did the books become un-illegal in the end?

The war is not over the books per se. It is over the many restrictions that the government puts on the people and the way in which they have become so desensitized. We have no idea about the fate of books after the war. What we do know is that people like Montag intend to keep books alive so that after the war, there could be a different attitude toward books.

No, the war didn't start because of the illegal books. The book banning, making them illegal is due to the changes in the government. The books are all about the way society has become oppressed. Montag's generation didn't grow up with books...... they were already gone. Society has already been oppressed. His curiosity and the things he seeks can be found in the books that have disappeared. Montag is searching for answers and explanations as to how things came to be in his world.

No, books aren't legalized in the end of the book. As the novel closes, the men walk away............ ready to rebuild the charred city. Each of them has memorized literature, and they're each ready to put it to paper when the time comes that's it's safe to do so.