13. The Reconquista of Spain took over 700 years and cost the lives of almost 10,000,000 people to accomplish
The Reconquista refers to an extensive series of wars lasting approximately 780 years, starting with the Umayyad conquest of Hispania in 711 and lasting until the fall of the Nasrid kingdom of Granada in 1491. In 711, the Muslim Moors crossed the Strait of Gibraltar to invade the Visigothic Kingdom of Hispania; this conquest would be completed by 719, whereupon the new realm of al-Andalus was created. Struggling to remain independent to the Islamic Umayyad Caliphate based in Córdoba, the Kingdoms of Asturias and Navarre served as the last bastions of Christianity in Spain. Winning several victories, notably the Battle of Toulouse in 721, these small states resisted the total conquest of Spain by the Moors.
With the fall of the Caliphate in the early 11th century, al-Andalus entered a period of prolonged civil war. Splitting into 34 competing kingdoms, the unified Christian kingdoms of the north were free to advance upon them one-by-one. By 1482, only the Emirate of Grenada remained and Ferdinand and Isabella launched the final war. Ending on January 2, 1492, with the surrender of Grenada, the Reconquista was finally completed and Spain turned its eyes towards the New World. At least seven million people were killed across the centuries of conflict, whilst in the aftermath of the Reconquista all Jews were expelled and Muslims were forcibly converted.