Why do you think there were so many battles on lands that were eventually ceded to the US government

In my opinion, there were many battles in lands that were eventually ceded to the United States because, because of the ideas emanating from the Doctrine of Manifest Destiny, the American government itself carried out military campaigns (as with Mexico, the natives Americans, Spain -Puerto Rico-) or promoted internal revolutions (as in the case of Hawaii, for example) in order to generate the necessary socio-political conditions to annex the territories, either through military conquest or through annexation.

c) troops march forward in close formation against newer, more accurate weapons

im going to go with b.