Although Duke Uvarov's plan could only be called mad, his judgment was actually quite accurate. The Danubian Principalities were simply too important to the Austrian Empire.
Historically, the main reason Austria betrayed Russia was that it believed Britain and France's promise of the Danubian Principalities. Austria's trial run at ruling the principalities, however, lasted only until the end of the Crimean War.
What the great powers called a fait accompli wasn't worth a damn in their eyes.
As Duke Uvarov saw it, they should use the Balkans as bait to keep Austria dangling, then swallow the Ottoman Empire whole.
Once the Ottoman Empire had been dealt with and the capital moved to Constantinople, they could easily take back the Danubian Principalities. After all, Austria had no other allies.
Even if the Austrian Empire had other allies, once the Ottoman Empire—the sick man of West Asia—was gone, they would have no reason to fight Russia to the death for Austria.
Nicholas I greatly admired Duke Uvarov's boldness, but the Danubian Principalities were just as important to Russia.
First was their strategic position. The Two Principalities controlled two mountain passes through the Carpathians, making them of extraordinary strategic importance.
If the passes were blocked, Austria would have to either take a detour or cross the Carpathians directly to attack.
Either option would put the Austrian Empire at a severe disadvantage. But once the Austrians were allowed through the Carpathians, they would have many more routes of attack to choose from.
Second, compared with the rest of the barren Balkans, the Two Principalities were fertile land.
Nicholas I didn't know that these two regions would one day become Europe's most important oil-producing areas, or that enormous veins of gold and silver would be discovered there in succession.
Besides that, they had everything the