Answer:
The Republican Party pushed for westward expansion between 1861 and 1865 for both political and economic reasons. On the one hand, because it needed access to new lands to exploit resources necessary to finance the war against the Confederacy, as well as to establish production centers outside the battle area. On the other hand, to take legitimate possession of those lands before the European powers (mainly France and Great Britain) that could take advantage of the turbulent situation in the nation to do it first. And finally, because in general the inhabitants of the region supported republican ideas, with which to include them in the nation would have given greater pressure to the Democrats at the time of the reunification of the country.