Why did both sides dig trenches on the western front

Which action by the us war department angered chief red cloud to the point that he refused to sign the treaty of fort laramie ? a) the killing of buffalo by the united states troops b) the appointment of troops to the powder river basin c) the burning of parts of the powder river basin d) the murder of chief red cloud’s wife

What major land feature is located at 0* and 20* e? a sahara desert b kalahara desert c congo basin d the alps

Can someone me write a paragraph on this topic i feel confused