Spain is considered by many, including a large part of Spanish population, to be a group of nations unified under a single State, much like Belgium, Switzerland or the United Kingdom. Despite this, the policy of many Spanish governments has led to a "Spanish nationhood" which is the one people identify with Spain internationally.
Modern Spain began to take form during the Reconquista, the struggle between the Christian kingdoms arising in the northern regions left unconquered by the Moors and the Muslim kingdoms into which Al-Andalus eventually split.
Through a policy of alliances with other European nobility and the conquest of most of South America and the West Indies, Spain began to establish itself as an empire. The Treaty of Tordesillas, negotiated by Pope Alexander VI between Portugal and Spain, effectively divided up the non-European world between these two budding empires. Massive amounts of gold and silver were imported from the New World into Spain's coffers. However, in the long run this hurt the Spanish economy much more than it helped it. The bullion caused high inflation rates, which undermined the value of Spain's currency. Additionally, Spain became dependent on her colonies for income, and when Queen Elizabeth I of England began to capture Spanish vessels on the way to and from the New World, Spain suffered massive economic losses. These effects, combined with the expulsion of Spain's most economically vital classes in the late 15th century (the Jews and the Moors), caused Spain's economy to collapse several times in the 16th century, bringing the Golden Age of Spain to a close.
After World War II, being one of few surviving fascist regimes in Europe, Spain was politically and economically isolated and was kept out of the United Nations until 1955, when it became strategically important for U.S. president Eisenhower to establish a military presence in the Iberian peninsula. This opening to Spain was aided by Franco's rabid anti-communism.
After the fall of the Roman Empire, Germanic tribes invaded the former empire, several turned sedentary and created successor-kingdoms to the Romans in various parts of Europe. Iberia was taken over by the Visigoths after 410.In the Iberian peninsula, as elsewhere, the Empire fell not with a bang but with a whimper. Rather than there being any convenient date for the "fall of the Roman Empire" there was a progressive "de-Romanization" of the Western Roman Empire in Hispania and a weakening of central authority, throughout the 3rd, 4th and 5th centuries. At the same time, there was a process of "Romanization" of the Germanic and Hunnic tribes settled on both sides of the limes (the fortified frontier of the Empire along the Rhine and Danube rivers). The Visigoths, for example, were converted to Arian Christianity around 360, even before they were pushed into imperial territory by the expansion of the Huns. In the winter of 406, taking advantage of the frozen Rhine, the (Germanic) Vandals and Sueves, and the (Asiatic) Alans invaded the empire in force. Three years later they crossed the Pyrenees into Iberia and divided the Western parts, roughly corresponding to modern Portugal and western Spain as far as Madrid, between them. The Visigoths meanwhile, having sacked Rome two years earlier, arrived in the region in 412 founding the Visigothic kingdom of Toulouse (in the south of modern France) and gradually expanded their influence into the Iberian peninsula at the expense of the Vandals and Alans, who moved on into North Africa without leaving much permanent mark on Hispanic culture. The Visigothic kingdom shifted its capital to Toledo and reached a high point during the reign of Leovigild, treated in some detail at its own entry.
The period of Visigothic rule saw the spread of Arianism briefly in Spain. In 587, Reccared, the Visigothic king at Toledo, having been converted to Catholicism put an end to dissension on the question of Arianism and launched a movement in Spain to unify the various religious doctrines that existed in the land. The Council of Lerida in 546 constrained the clergy and extended the power of law over them under the blessings of Rome.
A revived movement for the Christian unification of Spain was capitalized on by the "Catholic monarchs" (Reyes Católicos in Spanish) Isabel I of Castilla and Fernando II of Aragón in order to justify their invasion of Granada, the expulsion of the Jews and the forceful conversion of the Moors. In the 15th century, the Kingdoms of Castile and Aragon were united under Isabel and Fernando. These two able rulers ruled jointly and worked to consolidate the power of the monarchy at the expense of the nobility. During their reign, the castles of many nobles (symbols of aristocratic independence from the monarchy) were demolished, and a system of regular taxation was established. Fernando and Isabel established the basis for the unification of Spain religiously as well as politically and economically.