(Note, the reason I made this so short is because it's the introduction.)
This story starts during the reign of Marti I d'Arago:
Advisor: Sire, the people want you to fulfill the task of vassalizing Navarra.
Marti: How would we do that?
Advisor: There's one way. You can go to war against Navarra. Would you like to do that?
Marti: Most definitely.
Marti decides to reform his country to be more innovative before the war. However, other nations do not take this as a prestigious act:
It's only temporary... Marti decides to declare war on Navarra, and take it over. He takes his only army and moves it to Navarra. However, Navarra already entered his country. But the Marti is not focused on this yet.
The Queen of Brabant asks Aragon for an alliance during this war, which won't benefit Aragon, but the King of Aragon decides to accept the offer.
What use could this have... They had won the battle of Navarra, even with high attrition lowering the morale on Aragon's army. Noticing Navarra's secondary army in the province of Aragon, Marti recruits two cavalry regiments to take care of the army.
Aragon now decides to bring Sicily into the war:
Sicily could help me with this war. And gets insulted by Foix:
How dare you insult me! The siege of Navarra also goes well, and the King of Aragon annexes the nation, against the wishes of the people... will such an act be taken kindly?
Prestige is nice, I can even replace the lost prestige when I made this nation more innovative. The new empire:
The newly received province of Navarra will make this empire larger (sort of). (Sorry for horrible writing, I can't write good.)