ば

conditional form; If [A] then [B]

ジーベル！やっぱりあなたなの？どうしてこんなことを！
どうして？
人間にんげんたちが 俺おれたちにしたことを 考かんがえればわかるだろう？

Jiiberu! As I thought, it is you? Why are you doing such a thing!
Why?
If you think about what the humans did to us, then you would understand.