Whether or not the U. S. acquisition from Spain and expansion into Florida was justifiable?

It was justifiable, because it was a continuation of the process of spreading the country's territory.

Explanation:

United States after 1783. had the idea of spreading towards the West, but additionally wanted to circle their territory towards the south.Florida was a Spanish territory with great importance, because it allowed them connection with the Caribbeans.Of course, this enabled economical prosperity and spreading of trade links.