The idea of "repatriating" artistic treasures taken by imperial powers
sometimes
involves simplifying
history, focusing on only one injustice out of a history of many
such.
Projecting modern standards of right and wrong back into the past is
often misguided and simplistic. The principle that nations shouldn't
try to defeat other nations and take their land is a modern advance in
morality. We should campaign to uphold that principle against nations
that violate it today.
In the past, though, just about every nation got its land by taking it
from some other nation. Empires were generally created by subjugating
other nations, and that surely includes Benin. That was not merely
common practice, it was also considered acceptable. If we were to
judge their past conduct by modern standards, we would condemn
almost every nation.