These are in my opinion the key events in Spanish history (not in chronological order)
1. Moorish rule and the mixing of the cultures.
2. Rise of the Christian Kingdoms in the 11th, 12 and 13th centuries.
3. The Marriage of Ferdinand and Isabella in 1492. Unification of Castille and Aragon.
4. The Spanish Inquisition and the expulsion of the Jews in 1492.
5. Charles V becomes Joint Habsburg and Spanish Empire.
6. The Final Defeat of the Moors in 1492. Last Moor stronghold in Granada collapses.
7. Invasion by the Visigoths during Roman times.
8. Age of Discovery and the conquest of South and Central America in the 16th century.
9. The Spanish Civil War (1936-1939).
10. Loss of Colonies in South and Central America in the 1820's and 1830's.
11. Loss of the Spanish Armada (1588).
12. The Carlist War of the 19th century.
13. Financial Collapse in the 17th century.
14. Defeating Napoleon in the Peninsula War (with English assistance).
15. Death of Franco and the coming of Democracy in 1976.
16. The rise and fall of Roman power in Spain.
17. War of the Spanish Succession and the Rise of the Bourbons.
18. Charles V abdicates and hands over power to his son Philip II.
19. 80 Year War with the Dutch in the 16th And 17th century. Leads to Dutch independence from Spain.
20. Loss of the Rock of Gibraltar to the British.