The sioux and sitting bull led the attack on general george armstrong custer's cavalry at the battle of little big horn. why did the sioux take this course of action?
a) general custer wanted congress to outlaw the sioux's ritual ghost dance.
b) the transcontinental railroad was moving through the area the sioux inhabited.
c) the u. s. army was threatening to take over the sioux's gold mines, which were key to the native american economy.
d) the u. s. government had broken promises to let the sioux remain in the black hills and was attempting to force them from those lands.