History and an Open Future--According to Plan?

On the Fourth of July I decided to re-read David McCullough's masterful speech entitled "The Glorious Cause of America". The full speech is worth a read, but something in his opening thoughts (which I appreciate) made me ponder. He opens by stating:

"One of the hardest, and I think the most important, realities of history to convey to students or readers of books or viewers of television documentaries is that nothing ever had to happen the way it happened. Any great past event could have gone off in any number of different directions for any number of different reasons. We should understand that history was never on a track. It was never preordained that it would turn out as it did.

Very often we are taught history as if it were predetermined, and if that way of teaching begins early enough and is sustained through our education, we begin to think that it had to have happened as it did. We think that there had to have been a Revolutionary War, that there had to have been a Declaration of Independence, that there had to have been a Constitution, but never was that so. In history, chance plays a part again and again. Character counts over and over. Personality is often the determining factor in why things turn out the way they do."

My question arises by juxtaposing this idea (that history isn't preordained, that it didn't HAVE to happen the way it did, that there didn't HAVE to be a Constitution, etc.) with the LDS belief that God perhaps foreordained or at least "raised up" the founders to do what they did, that Nephi saw some of this continents' history in vision, and that the American Revolution was a prerequisite in order to prepare the way for the Restoration (as though it were on a track, which McCullough explicitly rejects because history involves chance).

How should a Latter-day Saint reconcile these seemingly contradictory ideas? Naturally, there is an important nuance between "foreordination" and "predestination", but how much of the "plan" has stayed on plan or has gone off plan? (Parenthetically, was "Plan B" concerning the 116 lost pages of the Book of Mormon because God knew what was going to happen or because He knew what was possible?)

Moving beyond history, it's an intriguing question to think about whether the future is truly open or already "fixed"--especially when prophecy is thrown in to complicate the picture. Sometimes Latter-day Saints start sounding like Calvinists (or maybe just fans of "The Adjustment Bureau"?) when they speak of God knowing the future as though it were predetermined, rather than allowing for real agency (not just the illusion of agency) and an open future.