Spain is a Kingdom in Western Europe during the events of The Tudors. It is bordered in the north by the Kingdom of France and the minor Kingdom of Navarre (a French vassal) and bordered in the West by the Kingdom of Portugal.
Although younger than its' neighbors England, France and Scotland (Spain has only recently achieved unification, through the marriage of Queen Isabella of Castille and King Ferdinand of Aragon, and Reconquista from the former Moorish Empire) it is the wealthiest and most powerful Christian kingdom, thanks to its' vast colonial empire in the Americas and inheritance of several territories in Italy, including the Duchy of Milan and the Kingdoms of Sardinia, Sicily and Naples. The recent conquest of the Aztec and Incan Empires in Mexico and Peru provides Spain with immense sources of silver and gold, though this also results in devaluing of Spanish coin. Originally ruled by House Trastamara, Spain has recently been inherited by House Habsburg under Charles V, who is also Archduke of Austria, Duke of Burgundy (the Netherlands) and Holy Roman Emperor. Thanks to Spain's vast wealth, powerful navy and formidable army, the Ottoman Empire is its' only real rival for power.
Due in part to its' sheer power, and ruthless enforcement of Catholicism through the Spanish Inquisition (which has resulted in the exile, torture, forced conversion and/or execution of its' non-Catholic subects), Spain and its' Austro-Burgundian co-states have many enemies. France has its' own claims to the Duchy of Milan and the Kingdom of Naples in Italy, and fears encirclement by Habsburg territory. The Ottoman Empire's conquest of Hungary and growing naval power threatens Spanish-Imperial interests in Central Europe and the Mediterranean, while the rise of the Protestant Reformation in Germany has caused many of the German States (including the Prince-Electors of Saxony and Bavaria, and the Duke of Cleves) to embrace Lutheranism, as a means of breaking free from Austro-Spanish influence. Although the Pope blesses Spain's efforts to stamp out Lutheranism, even Rome is wary of Spain's power; in 1527 ("Arise, My Lord"), mutinous Spanish-Imperial troops storm and burn Rome, and the Pope temporarily becomes Charles' captive. England, meanwhile, continues to vacillate between France and Spain as it suits them. Spain's only reliable ally is the Kingdom of Portugal, through Charles' marriage to Queen Isabella of Portugal.