A region of Africa, named for the river. Note that there are several states using the name Congo. The DPR Congo, formerly known as Zaire, is typically seen as a war-ridden hellhole in the West.
The original Congo was an African state closely allied with Portugal, but this Congo's territory lay more in the area of Angola.
Randomian Congo - Congo is notable in AH because it tends to come under the control of a very small, random European colonial power in the 19th century (mirroring Belgium in OTL). It is now something of an AH Cliché that Congo becomes ruled by countries like Aragon, Venice, Switzerland, Denmark etc.