As verbs the difference between united and amalgamated
is that
united is past tense of unite while
amalgamated is past tense of amalgamate.
As adjectives the difference between united and amalgamated
is that
united is joined into a single entity while
amalgamated is combined from two or more entities into one specific entity whilst retaining the defining characteristics of the original source entities.
As a proper noun United
is any of many football teams formed by the amalgamation of smaller ones.