Micronesia is the third of Dumont d'Urville's 1832 divisions and the one drawn on the least loaded criterion: the islands are small. It covers the Marianas, Palau, the Caroline Islands, the Marshall Islands, Kiribati and Nauru, spread across a stretch of the western Pacific larger than the continental United States and holding, in total, a very small area of land. Most of the languages are Austronesian, though not all from a single subgroup, so the grouping partly tracks a real relationship and partly does not.
Chamorro in the Marianas and Palauan are both Austronesian but sit outside the Micronesian subgroup proper, which is a good example of a regional label and a linguistic one failing to line up. What the region does have in common is the ocean and the problem it sets. Settling and holding islands this small and this far apart required navigation of a very high order, and the traditions built around it, the stick charts of the Marshall Islands and the wayfinding knowledge of the Caroline Islands above all, are among the most remarkable bodies of applied knowledge anywhere. The twentieth century was hard on the region. The islands passed between Spanish, German, Japanese and American administration, were fought over in the Pacific war, and Bikini and Enewetak in the Marshalls were used for nuclear testing, with populations removed and in some cases never able to return.