The Book Of Mormon - several curiousities

I do wonder how a Mormon would reply to my questions concerning the undeniably "modern" cast to the language in the parts of the book I have read so far (I am up to 3 Nephi). By this, I mean a distinct parallel between the rhetoric of the book and those of the early Revolutionary writers (Thomas Paine being the most obvious - and the most ironic). The time frame of the discovery of the plates which carried the Book - 1823 - is mere decades after the Revolutionary war ended, and many of the writers of the time were still publishing new works well into the 19th century.

The most common "sticks out like a sore thumb" word to me is "liberty". A concurrent reading of the Bible (I'm in the book of Numbers now) reveals no such sentiments. The Israelites had one leader, and later a succession of kings. It was quite literally "my way or the highway". Descended as they are supposed to be from the original Twelve Tribes, the people inhabiting the New World as "Promised Land II" are distinctly modern in their approach to government (a word also not mentioned in the Old Testament).

The Book of Mormon has always seemed fictional to me, and my reading of the book itself does nothing to dispel this notion.