Spain
The grandson of Ferdinand and Isabella was Charles.  When his grandfather died he inherited Castille and Aragon.  He also inherited many territories at the death of his other grandfather, Maximilian I of Austria.  Charles received from Maximilian the Austria state and the territories of Burgundy.  He was named Charles I in Spain, but he was elected as the emperor of the Holy Roman Empire, and was called Charles V, Holy Roman Emperor.  This made the empire bigger than ever.  However, it was not a single country, but a personal union of  many independent countries with a single King.  At first many Spaniards did not want Charles as their king, so they fought against him. However, he won.