Why did disease and warfare sharply reduce the Chamorro population after Spanish conquest?

Following the arrival of Spanish colonists in 1668, the Chamorro population experienced a catastrophic decline due to a combination of violent conflict and the introduction of foreign diseases.12

The reduction was driven by several key factors:

• Violent Resistance and Reprisals: The Chamorro people resisted Spanish efforts to impose Western colonialism and religious conversion. This led to a series of uprisings known as the Chamorro wars, characterized by revolts, sieges, and the killing of missionaries. In response, Spanish forces engaged in brutal military campaigns to subdue the population.2
• Forced Relocation: To consolidate control, the Spanish moved the native population into segregated villages and enclaves. During these forced relocations, many islanders were killed. Eventually, the Spanish forcibly removed the entire native population from islands such as Saipan and Rota, concentrating them on Guam.12
• Disease: The concentration of people into these settlements facilitated the rapid spread of diseases introduced by the Europeans, which decimated the population.2

By 1820, these combined pressures had reduced the Chamorro population from an estimated 50,000–100,000 to approximately 1,000.1