What modern-day nations constitute the Senegambia region today?

Question

On Wikipedia it says, "The region encompasses the modern states of Senegal, The Gambia, and Guinea-Bissau, as well as portions of Mauritania, Mali, and Guinea." However, I was told to not always take information from Wikipedia.
An Oxford bibliography states, "Senegambia, strictly speaking, comprises the nations of Senegal and The Gambia, although southern Senegal and the adjacent nation of Guinea-Bissau (Guiné-Bissau in Portuguese) have much in common in terms of climate and geography. "
I don't really know the difference between nation and countries because it says Senegal and Gambia are countries on some sites while on others they are nations.
Which ones should I use?

Answer 1

For most purposes, country and nation are used interchangeably.

Answer 2

Let me see