They set out in May 1804, and got back in September 1806. Ambrose wrote his book a few years before the bicentennial anniversary, and even today we're only 210 years behind them. And that's the first startling thing about the story. As recently as 200 years ago, if you floated down the Ohio River west towards the Mississippi, you were surrounded by hundreds of miles of pristine forest, with, here and there and at great distance from one another, a rough stockade or a one-street trading station with maybe a few hundred locals, all of whom had arrived there in recent years. Cincinnati was a really big city (but did it have more than a thousand people? The book doesn't tell), and it had been founded 15 years earlier.
And the area east of the Mississippi was mapped, known, and part of the United States. Seen from the perspective of where Lewis and Clark were going, it was civilised and tamed. Pretty soon it would even be boring and unattractive for the pioneering spirits who were escaping the stifling civilization of the Eastern seaboard into the unknown and untamed frontier.
They didn't have Whatsapp in those days, and Facebook was unreliable. As a matter of fact, as Ambrose reminds us early on, the the only type of communication anyone had ever dreamed of which was faster than a man's pace of walking, was if he was on horseback. Which means that from the day in May 1804 when Lewis and Clark started upstream from St. Louis (pop. 1000), they were out of contact. Once or twice in the coming years they sent back a few messengers, whom they never saw again and could only hope would arrive back in civilization; they themselves heard nothing from civilization until they appeared one fine September day back in St. Louis, two and a half years later.
In the interval they lived off the provisions they'd acquired in advance, and mostly, they lived off their wits and off the land, essentially reverting to hunter-gatherers. They were very good at being hunter-gatherers, but they'd also chosen a good place. The descriptions of the bountiful land they were moving through are, simply, astonishing. Much of the area is still bountiful, indeed, it's the breadbasket of the world, but it's tamed and controlled by humans. It was different 200 years ago.
So they made their way all the way to Oregon (which wasn't yet called Oregon), took a selfie on the coast of the Pacific, and walked back, proving that it was all there, that area, that there wasn't a combination of big navigable rivers that crossed it, and discovered a few hundred species of plants and critters previously unknown to the taxonomists.
Not part of mapped civilization, perhaps, but not empty of people. There were various tribes of Indians (that was the word used then, and until recently). Each time Lewis and Clark encountered a new group, they gave them a version of their standard stump speech, which needed to be translated through six or eight people, in the probably vain hope that the original English version would come out at the other end in some vaguely recognizable form. Here's the description of the first time Lewis gave it:
Lewis opened by advising the warriors to be wise and look to the true interests of their people. "Children", he continued, as Clark recorded his speech, "we have been sent by the Great Chief of the Seventeen great nations of America to inform you... that a great council was lately held between the great chief and your old fathers, the French and Spaniards". There it was decided that the Missouri River country now belonged to the United States, so that all those who lived in that country, whether white or red "are bound to obey the commands of their Great Chief the President who is now your only great father". (P. 156).And from there on the speech got worse.
That passage made me stop and think for a moment. In 1804, more than 90% of recorded Jewish history (so far) had already happened. More than 1,500 years of the interval between the collapse of the (western) Roman Empire and the rise of United Europe (such as it is) had already happened. The French Revolution was already history, and Napoleon was wandering around Europe causing uproar. Shakespeare had been dead almost 200 years. Jerusalem, considerably older than Cincinnati or even Virginia, was at one of its many lowest points, but had only a few decades left before it would begin growing beyond its walls, and with a Jewish majority.
210 years is a long time if you're building a family tree, but in terms of history, it's just yesterday. And just yesterday, the first organized white man ever to reach Iowa was preaching at the locals in terms that no kindergarten teacher would use today without blushing. All he was doing was preaching; the really bad stuff was yet to come. As Ambrose notes later in the book, the entire process of the western-moving pioneers regarding the Indians was simple: move out of our way or be killed. Since being in the way meant being on the continent, that left only the option of being killed - and indeed, they're effectively all gone.
Everything I read, I read with an Israeli perspective. Sorry, that's just who I am. The earliest proto-Zionist settlements were started in 1878, and they picked up speed in 1882. The distance in time between Lewis and Clark, first explorers of the western half of the United States, and the advent of Zionism, was 80 years. The final subduing of the American West (sometimes called the Closing of the Frontier) and early Zionism were, quite literally, simultaneous events. The original population of the United States are gone - gone from Massachusetts these past four centuries, but gone from the western half of the country all of, what, 150 years? Less even than that? Meanwhile, in Israel alone there are more Arabs today than there were in the whole country in the late 19th century.
Next time you hear an American enemy of Israel speechifying about the evils of invading someones land and then stealing it, too, ask them what their opinion is of Missouri. Or Oregon. Because it's the same time frame.
Or, if you'd prefer to simply read a book with a great yarn about a world that's gone, read this book.