Smallpox in the context of "Rinderpest"

The Spanish conquest of the Aztec Empire was a pivotal event in the history of the Americas, marked by the collision of the Aztec Triple Alliance and the Spanish Empire, with the latter being supported by its Indigenous allies. Taking place between 1519 and 1521, this event saw the Spanish conquistador Hernán Cortés, and his small army of European soldiers and numerous Indigenous allies, overthrowing one of the most powerful empires in Mesoamerica.

Led by the Aztec ruler Moctezuma II, the Aztec Empire had established dominance over central Mexico through military conquest and intricate alliances. Because the Aztec Empire ruled via hegemonic control by maintaining local leadership and relying on the psychological perception of Aztec power—backed by military force—the Aztecs normally kept subordinate rulers compliant. This was an inherently unstable system of governance, as this situation could change with any alteration in the status quo. A combination of factors including superior weaponry, strategic alliances with oppressed or otherwise dissatisfied or opportunistic Indigenous populations, and the impact of European diseases contributed to the downfall of the short rule of the Aztec civilization. In 1520, the first wave of smallpox killed 5–8 million people.

Population figures for the Indigenous peoples of the Americas before European colonization have been difficult to establish. Estimates have varied widely from as low as 8 million to as many as 100 million, though by the end of the 20th Century, many scholars gravitated toward an estimate of around 50 million people.

The monarchs of the nascent Spanish Empire decided to fund Christopher Columbus' voyage in 1492, leading to the establishment of colonies and marking the beginning of the migration of millions of Europeans and Africans to the Americas. While the population of European settlers, primarily from Spain, Portugal, France, England, and the Netherlands, along with African slaves, grew steadily, the Indigenous population plummeted. There are numerous reasons for the population decline, including exposure to Eurasian diseases such as influenza, pneumonic plagues, and smallpox; direct violence by settlers and their allies through war and forced removal; and the general disruption of societies. Scholarly disputes remain over the degree to which each factor contributed or should be emphasized; some modern scholars have categorized it as a genocide, claiming that deliberate, systematic actions by Europeans were the primary cause. Traditional interpretation of the decline by scholars have disputed this characterization, maintaining that incidental disease exposure was the primary cause. This is supported by evidence where 50-80 percent of the population died from waves of diseases caused by Europeans in places such as Mexico in the 16th century.

Science in the medieval Islamic world was the science developed and practised during the Islamic Golden Age under the Abbasid Caliphate of Baghdad, the Umayyads of Córdoba, the Abbadids of Seville, the Samanids, the Ziyarids and the Buyids in Persia and beyond, spanning the period roughly between 786 and 1258. Islamic scientific achievements encompassed a wide range of subject areas, especially astronomy, mathematics, and medicine. Other subjects of scientific inquiry included alchemy and chemistry, botany and agronomy, geography and cartography, ophthalmology, pharmacology, physics, and zoology.

Medieval Islamic science had practical purposes as well as the goal of understanding. For example, astronomy was useful for determining the Qibla, the direction in which to pray, botany had practical application in agriculture, as in the works of Ibn Bassal and Ibn al-'Awwam, and geography enabled Abu Zayd al-Balkhi to make accurate maps. Islamic mathematicians such as Al-Khwarizmi, Avicenna and Jamshīd al-Kāshī made advances in algebra, trigonometry, geometry and Arabic numerals. Islamic doctors described diseases like smallpox and measles, and challenged classical Greek medical theory. Al-Biruni, Avicenna and others described the preparation of hundreds of drugs made from medicinal plants and chemical compounds. Islamic physicists such as Ibn Al-Haytham, Al-Bīrūnī and others studied optics and mechanics as well as astronomy, and criticised Aristotle's view of motion.

A pandemic (/pænˈdɛmɪk/ pan-DEM-ik) is an epidemic of an infectious disease that has a sudden increase in cases and spreads across a large region, for instance multiple continents or worldwide, affecting a substantial portion of the human population. Widespread endemic diseases with a stable number of infected individuals such as recurrences of seasonal influenza are generally excluded as they occur simultaneously in large regions of the globe rather than being spread worldwide.

Throughout human history, there have been a number of pandemics of diseases such as smallpox. The Black Death, caused by the Plague, caused the deaths of up to half of the population of Europe in the 14th century. The term pandemic had not been used then, but was used for later epidemics, including the 1918 H1N1 influenza A pandemic—more commonly known as the Spanish flu—which is the deadliest pandemic in history. The most recent pandemics include the HIV/AIDS pandemic, the 2009 swine flu pandemic and the COVID-19 pandemic. Almost all these diseases still circulate among humans though their impact now is often far less.

The Plague of Cyprian was a pandemic which afflicted the Roman Empire from about AD 249 to 262, or 251/2 to 270. The plague is thought to have caused widespread manpower shortages for food production and the Roman army, severely weakening the empire during the Crisis of the Third Century. Its modern name commemorates St. Cyprian, bishop of Carthage, an early Christian writer who witnessed and described the plague, in his treatise On the Plague. The agent of the plague is highly speculative due to sparse sourcing, but suspects have included smallpox, measles, and viral hemorrhagic fever (filoviruses like the Ebola virus). The pandemic attacked everyone, "just and unjust", and the response to it has strong ties to Christian beliefs and religion.

The fall of Tenochtitlan, the capital of the Aztec Empire, was an important event in the Spanish conquest of the empire. It occurred in 1521 following extensive negotiations between local factions and Spanish conquistador Hernán Cortés. He was aided by La Malinche, his interpreter and companion, and by thousands of indigenous allies, especially Tlaxcaltec warriors.

Although numerous battles were fought between the Aztec Empire and the Spanish-led coalition, which was composed mainly of Tlaxcaltec men, it was the siege of Tenochtitlan that directly led to the fall of the Aztec civilization and the ensuing sacking and violence against the survivors. The indigenous population at the time was devastated due to a smallpox epidemic, which killed much of its leadership. Because smallpox had been endemic in Spain for centuries, the Spanish had developed an acquired immunity and were affected relatively little in the epidemic.