It’s the most westerly island in the Aleutian chain — closer to Russia than mainland Alaska — and was one of just a few U.S. territories, along with Guam, the Philippines and the nearby island of Kiska, taken by enemy forces during the war.

Source: https://japantoday.com/category/world/death-of-last-surviving-alaskan-taken-by-japan-during-wwii-rekindles-memories-of-forgotten-battle

The balloon had first flown over the Aleutian Islands, through Canada, and into Montana.

Source: https://www.independent.co.uk/news/world/americas/us-politics/chinese-spy-balloon-during-trump-biden-b2276504.html