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)

Look up a map of Portugal featuring regions and major cities, especially from this period. (previously link is dead)

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.