The large colony of West Africa comprised what are today Mauritania, Senegal, Mali, Guinea, Côte d’Ivoire (Ivory Coast), Burkina Faso, Benin, and Niger. From 1895 until 1943, each of the separate areas issued their own stamps; afterwards, stamps for the entire French West Africa area were used, often imprinted with the specific area’s name. In 1960, the countries were given independence.
Buying French West African stamps now is one of the great classifications of African stamp collecting: it encompasses a very large swath of Africa, both geographically and geopolitically. Much history about the continent can be gleaned just by studying and learning about FWA stamps.
The other factor is that getting together a French West Africa stamp collection is pretty simple and cheap. Except for some rare cases, nearly all FWA stamps can be had for relatively low cost. Obtaining examples of each kind, from each area, is a fun and rewarding experience.
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Note: The French name for the colony was Afrique Occidentale Française; this is often the term used in stamp sales.