In the 5c (concurrent with the sack of Rome) Iranian & Germanic tribes like the Vandals crossed the Pyrenees into Hispania fragmenting Roman control. Eventually Visigoths gained the upper-hand establishing Toledo as their capitol, until Iberia was overrun by Berber Muslims in 711 AD, who dominated the peninsula for nearly 800 years.

The small Christian kingdoms🔍, (like León, Castile, Aragon, and Navarre) slowly pushed the Berbers south🔍 over the centuries, but they weren't able to fully expel the Moors until 1492 after the marriage of Catholic monarchs Ferdinand & Isabella unified Spain, launching a cultural golden age in the 16c & 17c; an era of exploration spanning from the Americas, to Asia, Africa & Oceania. At one time, starting, with the Spanish Habsburg monarch Charles V, the Spanish kings also ruled the Holy Roman Empire.

In 1700 the Spanish Hapsburg's died out and with War of the Spanish Succession Spain and the Holy Romans went their separate ways & when Napoleon invaded in 1808, triggering the Peninsular War, (known in Spain as the War of Independence,) Spain lost nearly all it's overseas holdings essentially ending Spain's Empire🔍.

Constant war & revolt in the 19c + 20c resulted in two republics🔍, a restored monarchy, the Spanish Civil War, Red & White Terrors†† and the authoritarian Francoist / Nationalist Spain, which seriously stunted economic growth (only 1% GDP growth over 20 years) and eventual caused a widespread famine. General elections finally resumed with a constitutional monarchy re-established in 1978, (surviving a failed coup attempt in '81)

† "Kingdom of Spain" - additional overseas territories include Ceuta & Melilla, autonomous cities on Morocco's northern coast (though Morocco contests their sovereignty) &  the plazas de soberanía; five minor North African outposts; Peñón de Vélez de la Gomera, Peñón de Alhucemas, Islas Chafarinas, Isla de Alborán, & Isla Perejil (all 5 lack civilian populations.)

†† The Red Terror was a wave of anti-clerical, anti-right-wing pogroms, and class-based violence carried out by the left-wing Republicans at the start of the Spanish Civil War; the death toll included 50,000-70,000 civilians, 6,800-7,000 of which were clergy (almost 20 % of Spain’s clergy.)

     The larger, longer-lasting, but less chaotic White Terror, carried out by Franco’s Nationalist side consisted of ~100,000–200,000 executions. The terrors both rank in the top 5 most deadly intentional mass killing events of civilians in history.