What were the motives for the Europeans to imperialize Nigeria?

Answer 1

That's quite simple, gold, diamonds and iron ore. there are some of the largest mines in Nigeria. The Europeans sent many expedition parties ahead of any Imperial invasion and if you look at the areas of Africa that were 'invaded' to state a point, they were the areas that had something of worth, also there is a secondary effect in that the peoples of those areas were forced into slavery.

http://www.minelinks.com/alluvial/gold1.html

Answer 2

To take up "the white man's burden" and try to "civilize" them.