“American” is the official English word when referring to people or things from the United States, but it heavily implies that it means either all of North America or all of North and South Americas. Most other languages have different words for American (country) and American (continents). If there were a campaign to replace the word “America” with something else when referring to the US, what would you think of it?
So I checked and apparently, I am wrong in thinking this was the case for many countries. Mexico is officially the United Mexican States though. For “Congo”, you actually have two different countries: Republic of the Congo (aka Congo-Brazzaville) and Democratic Republic of the Congo (aka Congo-Kinshasa). The Congo is, in fact, a big river and the names and borders come from colonialism of course.
Indeginious activits apparently also use AmeriKa or some various to link it to it’s colonial or settler history (same with Kanada).