Saint Patrick’s Day

Several weeks ago, we celebrated Saint Patrick’s Day. I think it is very pleasant to see every one dressed in green and be part of this celebration. However, from the first day I arrived in the United States, I never understood why Saint Patrick’s Day in celebrated in the US and why so many people take part of it. From what I understood, Saint Patrick’s Day is an occasion for Irish people to celebrate Saint Patrick, the patron protector of the Irish population. The majority of the population of the United States is not Irish so why such an infatuation for this celebration? I even read that every year the city of Chicago dyes the Chicago River in green at this occasion (which I suppose can be very bad for the environment and contribute to the pollution of the waters). This celebration surely originates from the Irish immigrant living in the United States. However, the Irish population is mainly concentrated in Boston and its area so I still find very interesting to see how a celebration introduced by Irish people in a certain region of the vast territory of the United States was able to spread through the entire continent (I assume Saint Patrick’s Day is celebrated everywhere in the US). On the other hand, in France I never hear of Saint Patrick’s Day and I think everyone will agree to say that France is relatively closer to Ireland than the United States is. Still if someone can explain me more in detail the origin of this celebration and why a lot of people in the United States celebrates it, it would be very helpful!!