The history of Aragon is one of independence, despite being a part of Spain for more than 300 years.
To a translation services worker like me, however, Aragon has a deep and rich history, a history you have to know fairly well if you have any hope of translating anything from old Aragonese to a modern language, or who wants to understand a private document written by someone living in the Aragon area who has been influenced by family or friends who still speak Aragonese. It's not a dead language, after all - so it has the potential to inform and influence the modern world, and as such is worth studying.
From Many, One
Like France and German, Aragon formed from several tribal mini-kingdoms. Up until the 11th century, these tiny units were subject to constant invasion and deprecations by the Franks to the north and the Moors to the south, and in the earliest years of the 11th century banded together for mutual protection and profit. Initially the kingdoms of Aragon, Sobrarbe, Ribagorza, and the duchy of Castile united under the name Kingdom of Navarre. In 1035 the King of Navarre, Sancho, died and the kingdom split into two. Sancho's son Ramiro I was named king of Aragon, and the modern sense of Aragon began.
Aragon was a belligerent country then and quickly conquered many of the surrounding territories. Curiously, Aragon had a strong sense of Rule of Law in a time when most monarchs cited God as their authority and claimed autocratic powers.
But in Aragon the King was required to swear to uphold the laws, was considered officially simply the first among peers in the nobility, and there was actually an official who judged all of the king's orders against the laws. The motto of Aragon at the time was "Before the king, there was the law."
From Two, Spain
Aragon continued to be a major European power until the dynastic union with Castile in 1469. King Ferdinand of Aragon married Queen Isabella of Castile, uniting their kingdoms under one family. This formed the foundation of the modern state of Spain, and Aragon's importance as an independent region declined as Spain's prominence grew, but Aragon remained ostensibly a separate kingdom until 1707, when King Philip V of Spain invaded the area and subjugated Aragon to Spanish rule officially.
In the modern era, Aragon has remained part of Spain but has continuously indulged its independent character. During the Spanish Civil War Aragon never officially declared independence but hosted many enemies of the Spanish government and anarchist communes, working actively against official Spanish interests.
In 1982, when Spain was reorganised under more democratic principles, Aragon became an "autonomous state" within Spain. This appropriate situation continues today.