What are the differences between actual Roman Catholicism and American Catholicism?
Please point out the historical, political, cultural and belief differences.
You can also provide me with some web-links.
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American Catholic and Roman Catholic are two completely different concepts.
Roman Catholicism refers to a particular rite of the Catholic Church. There are a number of Catholic rites, but whichever one you practise, you still take the pope as the ultimate authority. Non-Roman rites include: Chaldean (mainly Iraq), Antiochian (mainly Syria and Lebanon) and Armenian (Syria, Lebanon, Turkey). There are also a couple of cities in Europe which use their own, non-Roman rites. One major difference between rites is the liturgical language that is used; Chaldeans and Syriac Catholics will use Syriac while Armenians will use Armenian. Roman Catholics use Latin as their liturgical language. The beliefs of Catholics belonging to different rites are not the difference; it is more how they practise their religion.
An American Catholic is a Catholic who is an American citizen. An American Catholic can be of any rite, usually depending on his or her ethnic or national background. A Chaldean with American citizenship will be a Chaldean-rite Catholic and an Italian American will be a Roman Catholic.
There is also an American Catholic Church, which has no connection to the original Catholic Church and has very few members. It is not recognised by the Catholic Church and it does not recognise the pope. If you meant this in your question (it is not clear), then the main difference is that the American Catholic Church rejects papal authority.
There really aren't a lot of differences, and that's by design. The Catholic church is just about the most top-down organization in the world. All the Bishops are appointed by Rome, and could be (and often are) from anywhere in the Catholic world.
Now it is true that American Catholics have personal beliefs that are quite different from the Pope and his college of Cardinals. The most famous difference is over contraception. The Catholic Church is just flat out against it (they are even against "non-procreative sex acts"). However, the vast majority of American Catholics don't believe this. One poll said 90%.
However, the Pope's line in Rome is officially the Church's line here in America. So officially there is no difference.