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Recurring theme for commentators of the Russo-Ukrainian War that the Dniepr will be the new border, it will be the line where the front stops.
I do agree that it is convenient to imagine it to be and attractive to imagine that.
This belief is strong all over the globe, and I have to call it a trope, that rivers are great borders, a natural separators, barriers when it comes to nations, countries, states, warring parties. And there are a couple of examples where a river is a border between two countries, and historically during wars (such as WWII) often along rivers were the lines where the front stabilized (for a while at least). Romanians are all for the fact to move their borders up to rivers and consider those as their natural borders.
But this is a misconception. There is some truth to it as I mentioned but rivers aren't separators, rivers always connected civilizations. In the antiquity was there Eastern and Western Egypt? No. There was a Lower and Upper Egypt - connected by the Nile. The Mesopotamian states were devided to Sumer south and Akkad north, both ethnicity spreading left and right. The Habsburg monarchy formed along the Danube on both sides.
Real barriers are the mountains. The Pirenese, the Alps, and yes, the Carpathians - ask the 4th Ukrainian front that was tasked to break through in the NE Carpathians where the 6th German and the 1st Hungarian armies held the mountains. Rivers, yes they can be convenient to cross, but mountains can be made impossible. It's the Himalaya that separates India and China, not the Indus.
The South Russian steppes are riddled with large rivers. Dniester, Dniepr, Donets, Don, and the Volga itself. None stopped the steppe people ever.
So yes, the Dniepr is a big wide blue line and looks like a great divide and it is possible that the final line at least partially will settle there, but not because rivers are so great static barriers. It is the ethnic division that could play more role why Russia wouldn't want the western regions.
But even now, Russia claims Kherson, which major, important parts on the other side of the Dniepr. And what about Odessa?
So I believe: yes, but not really.