Why Spain has never invaded/kept Portugal under its reign?

by surinam_boss

It's very strange that such a huge power like Spain in the XV century never invaded Portugal. They were allied with the British and it would've been a great gate towards Americas

Searocksandtrees

hi! hopefully someone can drop by with comments on the issues raised here, but meanwhile, you can get started with the FAQ

Portugal and Spain on the Iberian peninsula

... and a few additional comments

How did Portugal survive as a enclave within Spain?
Why did Spain never conquer Portugal? How was it able to maintain its independence?
Why have Portugal and Spain's borders remained so stable over centuries?
Was there ever much of a history of Spain trying to annex Portugal?
How is it that Spain and Portugal have such distinct histories and languages even though they have shared the same peninsula and the territory for so long?

gerrardistanbul

Could you possibly elaborate slightly on your question? Portugal was effectively under Spanish rule during the Iberian Union from 1580-1640. Are you asking why it didn't last?