Was the ideology justifying American aggresion in 1846-48 similar or different from the same ideology of 1896

There were both similarities and differences between the
ideologies behind these two wars.

Both of the wars were
clearly justified by the idea of American superiority.  This superiority was seen both
in societal and in racial terms.  In other words, both wars were underpinned by the idea
that Americans were racially superior to the people of Latin America and that Americans
had a better society (government, religion, etc) than was present in Latin
America.

The major difference is that the ideology of 1896
was more focused on the alleged need to help the people who were being conquered.  There
was no real idea of taking up the "white man's burden" in the conquest of Mexico.  By
1896, there was clearly a felt need to justify imperialism as something that would work
to the benefit of those who were conquered.