The reassertion of Russia’s greatness has been a motif of Vladimir V. Putin’s presidency, and his projection of military might and cyberpower is in part why Russian-American relations are at their lowest point since the end of the Cold War.

So the 150th anniversary on Thursday of Russia’s sale of Alaska to the United States — an event that few Americans may notice — was a day of mourning for some hard-right Russian nationalists who see the transaction as a gigantic blunder by the ailing czarist empire, one that reverberates as the major powers vie for influence over the Arctic and its natural riches in an age of climate change.

“If Russia was in possession of Alaska today, the geopolitical situation in the world would have been different,” Sergey Aksyonov, the prime minister of Crimea, told a Crimean television network this month.