This Is the Check That Paid for Alaska

It's not about the oil; we have Texas and North Texas for that. Without Alaska, we wouldn't have moose burritos.

"No, we don't cash checks numbered under a thousand. It's our policy."

Back in the 19th century, Canada wasn't our close ally. US military invaded Canada in the 1812 war with Britain. In 1846 the Oregon boundary dispute could have resulted in an all-out US/Canada land war, too. There was no way to know, back then, that Canada would become an ally. And even if someone had that foresight, avoiding the intervening years of hostilities would surely have been worth the cost. Domestic control is important for investment, too. Would all the US oil companies have gambled their entire assets on the Alaskan pipeline, if Alaska was held by a foreign country? Canada didn't have the assets to make that happen, and likely not the political will, either.

Not to mention that we don't know what the future holds, today, and if relations with Canada go bad for any reason, Alaska could again be a critical piece of land to posses. Canada puts restrictions on a number of their domestic industries, from maple syrup to banning large fresh water exports, etc. They could similarly change their policy on oil exports at any time.

Today, with Arctic oil/gas extraction looming larger, it's only because of Alaska that the US will be entitled to a large share of the pie, mostly a 3 way split between the US, Canada and Russia, which could be massively profitable.