A people

I read a quote of Mark Twain on wikipedia and i got confused with this part:

I wanted the American eagle to go screaming into the Pacific …Why not spread its wings over the Philippines, I asked myself? … I said to myself, Here are a people who have suffered for three centuries.

Why does he say “a” people?

‘People’ (singular) is used to refer to an ethnic or national group. Its plural is ‘peoples’: The peoples of Asia are 70 % of the world’s population.