Sweden sold off Swedish Pomerania at the end of the Napoleonic wars in a good piece of business. Initially they wanted to swap it for Norway with Denmark, but as the Norwegians balked they never handed it over and then the Prussians swooped in and bought that and other bits and pieces off Sweden and Denmark.

It was a good piece of business as the defense of it would have cost resources but it still would have been a walkover against a serious opponent. And they would have lost it soon enough, at the latest in 1848 and the upheaval then.

Many of those instances are selling what one is unable to hold. There was, for instance, ~zero chance that France would end up actually retaining the Louisiana Purchase lands in perpetuity, so the only question was whether they'd get something in return (and they quite needed the money at the time), or lose them in an expensive war later.

It's debated whether the US has made money off of the purchase of Alaska from Russia or not[0].

The question of whether the US has made a return is not exactly the same as whether Russia profited off of the transaction (the costs to the US of governing the property may not be representative of what Russia would have paid), but they are related.

[0] https://en.wikipedia.org/wiki/Alaska_Purchase

The Dutch Republic traded New Amsterdam (modern day New York) to England in exchange for Suriname. But after England had demonstrated that they could take New Amsterdam whenever they wanted, so getting something in exchange was certainly better than nothing.

It's almost always true that holding real estate is better in the long view than selling it. I expect my house to continue to rise in value indefinitely. Doesn't mean it's never the right call to sell it.