Why did Christopher Columbus believe that Cuba was part of Asia?

Christopher Columbus believed that Cuba was part of Asia primarily due to his reliance on inaccurate geographical calculations and his interpretation of historical texts.12

His conviction was shaped by several key factors:

• Inaccurate Distance Estimates: Columbus significantly underestimated the circumference of the Earth by using an incorrect value for a degree of latitude and relying on a chart by the geographer Paolo Toscanelli. By combining this with an exaggerated view of the east-west extent of Asia, he concluded that the distance across the Atlantic was much shorter than it actually is.12
• Geographical Misconceptions: Based on his reading of Marco Polo’s Travels, Columbus believed that the lands of the East, including the island of Cipango (Japan), extended far around the globe. When he reached Cuba, he convinced himself that he had arrived at the Cathay mainland, even though he lacked evidence of the great cities described by Polo.123
• Confirmation Bias: Columbus was so committed to his goal of reaching the wealthy trading regions of Asia that he insisted his crew swear an oath that Cuba was the southeast promontory of the Asian continent. He remained steadfast in this belief throughout his early voyages, failing to recognize that he had encountered a previously unknown part of the world.23