Russia offered to sell Alaska in 1859 because they were in debt from the Crimean War. The U.S. did not initially make this purchase because of Civil War debts.
At the time of the purchase, America was still in a expansive mood. No one knew of any resources in Alaska then. Oil was not a big one for anyone. Alaska was even called "Stewart's Folly" (Stewart was a secretary of the interior) and a waste of federal money. (The dang place went for about 10 cents per square mile!)
Stewart wanted to simplify the map of North America and to block the British in Canada from further expansion as the USA and the British Empire were still not the best of friends.
Also, the Russians felt they could never have a firm hold on such a distance colony, needed some cash in a hurry because of a pending war with the Ottoman Empire and the Tzar on the throne at the time was a bit wacky.
It was strictly a move by the USA to secure the last major piece of real estate still open in North America.
I will do the work one after the other and will need a hand by employing a secretary to write down the name of people for me to start working with and also attend to them first because first come first served
Explanation: At the bottom of the eye there are millions of cells like cones and rods that collect the different elements of the spectrum of sunlight and change them into electrical impulses that then send them to the brain through the optic nerves. The cones are concentrated near the retina. The cones are responsible for the color vision.