Law by European monarchies to legitimise the colonisation of lands outside of Europe

The law you're referring to is known as the Doctrine of Discovery, which was a series of papal bulls, or decrees, that gave Christian explorers the right to claim lands they 'discovered' and lay claim to those territories for their Christian Monarchs. This was used as a legal and moral justification for colonial expansion into non-European lands during the Age of Discovery.

Here are the steps:

1. The Doctrine of Discovery originated from a series of papal bulls issued in the 15th century, such as the Dum Diversas (1452) and Romanus Pontifex (1455), which granted Portugal the right to conquer Saracens and pagans.

2. In 1493, following Christopher Columbus's first voyage to the Americas, Pope Alexander VI issued the bull Inter Caetera. This granted Spain the exclusive rights to conquer newly discovered lands in the Americas.

3. These papal bulls essentially stated that any land not inhabited by Christians was available to be 'discovered', claimed, and exploited by Christian rulers. If the 'pagan' inhabitants could be converted, they might be spared. If not, they could be enslaved or killed.

4. The Doctrine of Discovery was primarily a European concept, but it was adopted by other nations, such as the United States. It has been used to justify the dispossession of indigenous peoples of their lands.

5. The Doctrine of Discovery has been widely criticised and is considered a significant source of the injustices suffered by indigenous peoples. Today, many international legal scholars argue that the Doctrine is a violation of contemporary international law.