republican
The word 'repubblicano' is used in Italian to refer to someone or something that relates to republicanism or to the Republican Party in Italy, similar to the way 'republican' is used in English to refer to related concepts in the United States.
My uncle is a convinced Republican.
In this sentence, the word 'repubblicano' is used to describe someone's political affiliation. It is similar to expressing political beliefs in English. The sentence indicates that the speaker's uncle is firmly committed to his Republican beliefs.
The Republican system is very different from the Monarchy system.
Here, 'repubblicano' is used to describe a type of political system. In Italy, 'repubblicano' can refer to the system of government as it contrasts with a monarchy, rather than referring strictly to a political party.
I have read a book about the history of the Republican party.
In this instance, 'repubblicano' is used as part of the name of a political party. It is the equivalent of referring to the Republican party in the United States. The phrase suggests that the speaker has read an in-depth explanation of the party's history.