The two best books about Portugal and Portuguese History related to USA,  that the Academy of Codfish of New England has already bought to offer copies to the Libraries of New England are:

(1) Eyewitness to Portugal, Azores and Madeira 
By DK Company form England. We will give you more information about it in the near future

(2) The Portuguese in the formation os the USA
by Manuel Mira. We will also give you more information about this book