Short answers, pulled from the story.
The Spanish Empire began in 1492 when Christopher Columbus sailed west under the banner of the Catholic Monarchs, Ferdinand of Aragon and Isabella of Castile. Their marriage created a personal union that merged the economic and military power of Iberia, setting the stage for centuries of expansion.
The Spanish Empire conquered the Aztec Empire in 1521 and the Inca Empire in 1532, establishing the Viceroyalty of New Spain in 1535 and the Viceroyalty of Peru in 1542. These conquests facilitated control over territories in western South America and Mexico while facing resistance from the Mapuche people for centuries in the Arauco War.
The Spanish Habsburgs, starting with Charles V, inherited a vast empire that included the Castilian empire in the Americas, the possessions of the Crown of Aragon in the Mediterranean, lands in Germany, the Low Countries, Franche-Comté, and Austria. They pursued goals including undermining the power of France, containing it in its eastern borders, and defending Europe against Islam, notably the Ottoman Empire in the Ottoman, Habsburg wars.
The Spanish Bourbons, starting with Philip V in 1700, implemented reforms to reorganize the institutions of the empire to better administer it for the benefit of Spain and the crown. Centralization of power, beginning with the Nueva Planta decrees against the realms of the Crown of Aragon, was to be for the benefit of the crown and the metropole and for the defense of its empire against foreign incursions.
The Spanish Empire began to disintegrate in the early 19th century, with the Spanish American wars of independence (1808, 1826) triggered by the power vacuum created by Napoleon's invasion of the Iberian peninsula in 1808. The Spanish, American War in 1898 marked the end of its global empire, with the destruction of Spain's Pacific and Caribbean fleets at Manila Bay and Santiago de Cuba severing supply lines.
The Spanish Empire's final territories in Africa, including Spanish Guinea, Spanish Sahara, and Sidi Ifni, were lost in the mid-20th century, with Spanish control of Spanish Sahara enduring until the 1975 Green March prompted a withdrawal, under Moroccan military pressure. The last territories in the Americas and the Pacific (1833, 1898) were lost in a series of conflicts and treaties, with the Treaty of Paris (1898) ceding Cuba, Puerto Rico, and Guam to the U.S.