Ixalan

From the introduction:

The Sun Empire is a powerful civilization that dominates the eastern coast of Ixalan. The empire’s fierce warriors are supported by priests who wield the power of the sun and command the mighty dinosaurs that inhabit the continent. A new ruler has brought the empire into an era of expansion, seeking to reclaim the lands in the continent’s interior that it once held. At the same time, a foreign incursion into those same lands sparks a search for the artifact known as the Immortal Sun, which the people of the empire view as a potent symbol of their identity.