Why is it der Nigerianer?

Nigerianer ends in -er, and most nouns ending in -er are masculine: in a German dictionary, 86% of them take der.

All nouns ending in -er
Sense 1
der

Meaning

[1] Citizens of Nigeria

[1] Staatsbürger von Nigeria

Examples

[1] These two Nigerians are the farmers from whom we were related to our business in Berlin

[1] Diese beiden Nigerianer sind die Bauern, von denen wir Waren für unser Geschäft in Berlin beziehen.

Declension

1 Singular Plural
Nominativ der Nigerianer die Nigerianer
Genitiv des Nigerianers der Nigerianer
Dativ dem Nigerianer den Nigerianern
Akkusativ den Nigerianer die Nigerianer

Pronunciation

Dictionary entries include material from Wiktionary. Wiktionary