In short, the beginning of us joining the Modern era.
In 1800, we were pretty much agricultural. But thanks to British hostility, we were forced to develop industries. We really should send them a nice Hallmark card to thank them. That played a crucial role in making us what we are.
The last battle in the War of 1812 is famous. But what it ought to be famous for is that we had a bunch of American made cannon, and that helped a lot.
In 1844, Sam Morse demonstrated the telegraph to a stunned Congress. Soon messages could travel across the country in minutes instead of weeks. We would later lay cable across the Atlantic to do the same thing. The War of 1812 ended in Belgium, but no one here knew. That famous last battle was fought after the war officially ended. Getting killed after a war is over is just so annoying.
Not long after that, when the presidency of Andrew Johnson ended, he went home by train. That was a first.
In the space of 2 generations, we went from an agricultural economy, to a thriving industrial economy.
All that technology helped bring the country closer together.
This book I am reading is part of the Oxford History of the United States series. If the others are as good as this, I'll be reading more.