Why in the novel Uncle Tom´s Cabin they called Tom as Uncle? Is the word uncle a kind of cultural tradition? It is something particular of the United States?

I'm going to go out on a limb here and suggest that the word "uncle" became symbolic for all black slaves at the time. Tom was a slave that was completely loyal and subservient to his first master even letting himself be sold rather than escape. This subservience has become synonymous with the word "uncle" when used in this context. I'll provide a link that will give you a bit of history that might help to the understanding of your question.