1. Portugal was formed before Spain.

2. Portugal was recognised by the Roman Catholic Church 1179. The united Spain formed by merging the kingdoms of Castilla and Aragón was established only in 1516, after they ousted the Muslim rulers in Granada in 1492.

3. Portugal did merge briefly with Spain in 1580 when the Portuguesse King Henrique died heirless. Philip I to Philip III of Habsburg (Spain) ruled both territories.

4. Philip IV lost Portugal to Duke of Braganza João IV in 1640. But the war lasted until 1668 before Spain admitted its formation. Peace treaty was signed between Portugal and Spain, mediated by Charles II of England. In between, Portugal signed on with several European rivals of Spain who preferred not to have Spain control the entire Iberian Peninsula.

5. Spain kissed Portugal bye bye, but still engaged in dispute with Portugal over Olivenza, a border area, until today.

Yeah, and Spain's tercios moving into Portugal and the Azores had something to do with that deal too.

Philip I?

Portugal was annexed by Spain in 1580, during the reign of Philip II.

Sorry. My mistake.

He was Philip II of Spain but known as Philip I of Portugal, like James VI of Scotland was also James I of England.

Boy, I do love this kind of questions....

First of all, there were two attempts from Spain (one from Castilla-Léon and one from Spain as we know it today, to be more precise) to conquer Portugal, both due to dinastical quarrels in Portugal, in 1383-85 and 1578-80. This last one was successful, since the rightful heir, the Duke of Parma, gave his rights to Philip II of Habsburg.

On the other hand, there were at least five attemps of Portuguese conquest of Spain, two by marriage, two due to spanish dinastical problems and just simply because the Portuguese king wanted Spain... Of course, all of them failed.

As for the spanish successful attempt, it had been proved during the middle ages that although superior in numbers, the Castillans/Spanish were never as strong as their neighbours, who saw in the spanish one of their main courses, along with arabs and french. So old Philip took a wiser decision and simply briebed Portugal's nobility, who then elected him King. A bit like his own father Charles V in his bid to become Holy Roman Emperor.

ARG

 Now I'm thinking I don't know much about the Portuguese. Just wandering what is the origins of the Portuguese and how they differ from say the castillans (noting that spanish is hardly a race). 

Alfonso VI, King of León, conquered the land as far as river Tajo and, in 1094 gave the "Terra Portucalense" as a county to Enrique de Borgoña, married with his bastard daughter, Teresa.

When Alfonso died he declared Portugal independent. He acted as an independent during the crisis in the kingdom of Castilla-León. When Enrique died his wife declared herself Queen and fought against Urraca, Queen of Castilla-León. Portuguese nobility rebelled against  Teresa, supporting her son, Alfonso Enríquez. He took the title of King as Alfonso I Enríquez (1139) after defeating her mother in Sao Mamede (1128) and a muslim army in Ourique (1138), and was recognized as that by Alfonso VII of Castilla and León in 1143.

The question should be 'why did Portugal never join Castile?'

The Portuguese language was seperate from Castillian and Leonese, but indistinct from Galician at this period of time. Some Galicians still say that Portuguese is really Galician modified due to moorish influence.

Well, dialects derived from Latin were the Castillian, Catalan, Astur-leonese, Navarran-aragonese, Galaic-portuguese and Mozarab.

Mozarab was the romance language spoken by the Christians, and the low classes in the muslim lands, Galaic-portuguese has derivated in current Portuguese and Galician, Astur-leonese has became Bable (in Asturias) and Leones (spoken in some places in León), Navarran-aragonese has derived in aragonese.