I started reading The Maias and quickly found myself lost during references to Portuguese history. I'm sure I will find more things I'm ignorant about, but for starters here are a few links that help make sense of the background events in the book:
Portuguese history: Fourth Dynasty (1640 - 1910) at Wikipedia
More detail at Wikipedia about The Liberal Wars (1828 - 1834)
A map of Portugal featuring regions and major cities
Update: Some helpful background can also be found in The Political History of Nineteenth Century Portugal. Also includes some description and discussion of Regenerationist movement.
Update 3 Oct 2011: Thanks to Amateur Reader for pointing to Michael Wood's review in the London Review of Books.