Answer:
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.