Who declared himself sapa Inca in 1438?

In 1438, Pachacuti declared himself Sapa Inca, marking the beginning of the expansion of the Inca Empire. Under his leadership, the Incas transformed from a small kingdom into a powerful empire, significantly expanding their territory and influence in the Andean region of South America. Pachacuti is also credited with significant administrative and architectural developments, including the establishment of Cusco as the empire's capital.