The border between the Black Sea and the Caspian is usually placed along the crest of the Caucasus Mountains, although it is sometimes placed further north. Asia–Oceania boundary The border between Asia and the region of Oceania is usually placed somewhere in the Malay Archipelago. The Maluku Islands in Indonesia are often considered to lie on the border of southeast Asia, with New Guinea, to the east of the islands, being wholly part of Oceania. The terms Southeast Asia and Oceania, devised in the 19th century, have had several vastly different geographic meanings since their inception. The chief factor in determining which islands of the Malay Archipelago are Asian has been the location of the colonial possessions of the various empires there (not all European). Lewis and Wigen assert, "The narrowing of 'Southeast Asia' to its present boundaries was thus a gradual process." Asia–North America boundary The Bering Strait and Bering Sea separate the landmasses of Asia and North America, as well as forming the international boundary between Russia and the United States. This national and continental boundary separates the Diomede Islands in the Bering Strait, with Big Diomede in Russia and Little Diomede in the United States. The Aleutian Islands are an island chain extending westward from the Alaskan Peninsula toward Russia's Komandorski Islands and Kamchatka Peninsula. Most of them are always associated with North America, except for the westernmost Near Islands group, which is on Asia's continental shelf beyond the North Aleutians Basin and on rare occasions could be associated with Asia, which could then allow the U.S. state of Alaska as well as the United States itself to be considered a transcontinental state. The Aleutian Islands are sometimes associated with Oceania, owing to their status as remote Pacific islands, and their proximity to the Pacific Plate. This is extremely rare however, due to their non-tropical biogeography, as well as their inhabitants, who have historically been related to Indigenous Americans. St. Lawrence Island in the northern Bering Sea belongs to Alaska and may be associated with either continent but is almost always considered part of North America, as with the Rat Islands in the Aleutian chain. At their nearest points, Alaska and Russia are separated by only . Ongoing definition Geographical Asia is a cultural artifact of European conceptions of the world, beginning with the Ancient Greeks, being imposed onto other cultures, an imprecise concept causing endemic contention