1598: Juan de Oñate makes a formal declaration of his Conquest of New Mexico

(Wikipedia) Juan de Oñate y Salazar (1550–1626) was a conquistador from New Spain, explorer, and colonial governor of the Santa Fe de Nuevo México province in the Viceroyalty of New Spain. He led early Spanish expeditions to the Great Plains and Lower Colorado River Valley, encountering numerous indigenous tribes in their homelands there.
Oñate founded settlements in the province, now part of the present-day American Southwest. Continued