The Anti-Racism Task Force at my church has been holding a series of online discussions. One involved the Doctrine of Discovery. I was vaguely aware of it. From the material:
The Doctrine “originally came from Papal bulls issued in the 1100s by popes, providing permission for Christian explorers to take land from non-believers and do with those people whatever they wanted. (e.g.Crusades, slavery, etc.)”
Daniel N. Paul created a First Nations history, worth reading in its entirety. He starts with a quote from Thomas Aquinas’ rationalization. “On the part of the Church, however, there is mercy which looks to the conversion of the wanderer… after [a couple of tries] that, if he is yet stubborn, the Church no longer hoping for his conversion, looks to the salvation of others, by excommunicating him and separating him from the Church, and furthermore delivers him to the secular tribunal to be exterminated thereby from the world by death.”
The Gilder Lehrman website describes in detail “The Papal Bull ‘Inter Caetera,’ issued by Pope Alexander VI on May 4, 1493… [It] played a central role in the Spanish conquest of the New World.” This follows a similar series of bulls by Pope Nicolas V a few decades earlier justifying the Portuguese slave trade.
The American version
The Wikipedia entry, also useful, notes: The doctrine… is a “concept of public international law expounded by the United States Supreme Court in a series of decisions, most notably Johnson v. M’Intosh in 1823. Chief Justice John Marshall explained and applied the way that colonial powers laid claim to lands belonging to foreign sovereign nations during the Age of Discovery. Under it, European Christian governments could lay title to non-European territory on the basis that the colonisers travelled and ‘discovered’ said territory.”
Look at the whole thing, which helps to explain the Monroe Doctrine and most especially Manifest Destiny. A legal debate found the Native Americans “to be in violation of international law through their resistance to Spanish exploration and missionary activities. By resisting Spanish incursions, Indians were, according to Vitoria, provoking war with the Spanish invaders, thus justifying Spanish conquest of Indian lands.”
I also highly recommend the links at the Upstander Project.
In a quick search, you’ll find a number of churches, governments, and other organizations repudiating the idea of the Doctrine of Discovery. These bodies recognize that the philosophy is not well known, and difficult to understand. But they recognize they’ve been advantaged, and that it still has an impact on modern-day dealings.
The Unitarians lowlight one of their own, Joseph Story. He was an Associate Justice of the Supreme Court at the time of the Johnson v. M’Intosh decision. The United Church of Christ addresses “Why it still Matters Today.” A group of Anabaptists noted: “Dismantling the Doctrine of Discovery can seem overwhelming for a lot of people. Here you can find a few foundational components to help break it down.”
This is a big topic, far beyond what I can fairly address here. But I believe it is worth your while to investigate.
Thank goodness for Greg Burgas. He 
I was well-pleased with who got into the class of 2022 for the Rock and Roll 
Damn. I’m going to miss Ken Screven. Ken, who reported for decades at WRGB/CBS6, the first African-American television reporter and news anchor in the Albany market, 