Why can't countries simply reclassify any part of someone else's land as an overseas territory to avoid decolonization processes?

Question

In the mid-20th century, during the era of decolonization, several European countries reclassified certain regions as "overseas territories" or similar designations rather than colonies. For example, Portugal claimed that Goa was an overseas province, not a colony, arguing it was not subject to the decolonization process. This led to significant debates at the United Nations, with the USSR vetoing Portugal's attempts to reclaim Goa under the guise of decolonization.

Similarly, France has maintained territories like French Guiana (an overseas department), Saint Martin, and Tahiti (overseas collectivities). These regions often have a different status and level of protection under international law compared to traditional colonies.

Are there any legal distinctions between overseas territories and colonies under international law to back these country's claims on their overseas territories?

Answer 1

The primary difficulty with doing that is democratic representation and consent of the governed. Residents of the French overseas departments are fully citizens of France regardless of ethnicity and vote in French elections, and their status has been determined by referendums among the local population; for instance, Mayotte became an overseas department after a referendum with decent turnout (comparable to US president elections, for instance) and quite high support for that status among voters, around 95%, not that there was not also some opposition. The argument for this is fairly simple: if two countries can voluntarily merge (as they can under international law), how could you force independence on a population that was opposed to it? The resulting independent country could easily just vote to merge. Note that the opposition to Mayotte being a part of France comes more from people who would like it to be part of Comoros, not from supporters of independence, although there are some French overseas collectivities with more equivocal support for continued French citizenship.

So to use this method to acquire territory, a country would have to persuade a majority of the residents of a territory to want to become part of their country, and would have to make them full citizens with voting rights; worst of all, they would probably have to continue to hold referenda in case sentiment turned in favor of independence, as has been the case in various French departments. This is not precisely conducive to the type of actions that most countries would engage in with respect to colonies, which is why most do not bother: Russia, for instance, invaded various parts of Ukraine before holding any referenda, and the USA does not give residents of Puerto Rico the same voting and other rights as residents of its 50 states; not coincidentally, both of those territories have been frequently described as colonies.

Answer 2

A colony is a form of military occupation. The colonizing nations sends settlers and troops to a region to establish long-term settlements, usually for the extraction of natural resources. These colonies are controlled and defended by the colonizing nation, whether against other national powers or indigenous natives, but neither the region itself nor its indigenous peoples are considered to part of the colonizing nation.

A territory is a formal but unincorporated part of the parent nation. Territorial land is considered to be 'owned' by the parent nation; territorial inhabitants (including indigenous peoples) are considered to be its citizens. Territories imply far greater commitments and costs for the parent nation, including defense, development of (non-utilitarian) infrastructure, representation in government, etc.

The colonial era ended largely because the World Wars sapped the resources of European nations, limiting their ability to control and suppress independence movements in colonized areas. Territorial status was generally only sought or granted in comparatively remote regions, because territorial status entails defense. No European nation wanted to be obligated to fight in the wars that would inevitably occur as newly-formed (ex-colonial) nations tested each other's borders.