In 2025, a small, indigenous nation that calls itself the “people of many colors” will go home for the first time in 80 years. Their return will drive a movement of indigenous peoples across the Amazon rainforest fighting for legal titles to their ancestral territories, and winning. These victories will have global significance.

The Siekopai lived for centuries along what is now the border between Ecuador and Peru in the western Amazon. In the 1500s, they were a powerful civilization with their own unique varieties of corn and an army capable of defeating the Portuguese conquerors and stopping their advance. Later, however, they were decimated by disease, enslaved by rubber tappers, and forcibly relocated to Jesuit missions. Approximately 80 years ago, a war between Ecuador and Peru displaced the remaining Siekopai. When the years of conflict waned, in 1979, a new, if contested, border cut through their homelands. The Siekopai now number about 1,950 survivors, with 750 in Ecuador and 1,200 in Peru.

In Ecuador, indigenous nations are in a landlord-tenant agreement with the Ministry of the Environment. There are now nearly 5 million acres of indigenous rainforest territories locked in “protected areas” within the Ministry of Environment’s control. This gives the government, for instance, the power to grant drilling rights, as it did in the Yasuní National Park, or to change the nature of the tenant agreement, which they did when the Cuyabeno Wildlife Reserve was created, denying indigenous people the right to hunt, fish, or garden and effectively making them trespassers in their own land.

In Peru, the government leases land to indigenous communities indefinitely for various uses based on the type of soil. On...