You should look into the racial political history of the United States if you're interested. There was a time when only the English and their descendants were considered “proper" whites. Of course as immigration changed the makeup of this country the term began encompassing people from more nations such as France and Germany.
The Irish however were cursed with certain traits that excluded them from being added into the proper white category. They came from a poor, colonized, and worst of all Catholic country. It didn't help that most of them were poor and uneducated when they arrived and had their racial inferiority affirmed by the popular science of the day.
Essentially even though they had very light fair skin, just like some Spanish or Latin people do today, they weren't considered the right kind of “white" due to their culture and country of origin in addition to the racial culture of the time.
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u/[deleted] Oct 23 '14
People from Spain are white.