A more thorough explanation:

Terra nullius is a term used in international law to describe a piece of land that is not owned by any state or entity. It is often used to legitimize state occupation and colonization of land that is already inhabited by a nation or minority.

When a land is declared as terra nullius, it can legally be occupied and acquired by another nation under the doctrine of discovery, which is a legal method of acquiring territory approved by the International Court of Justice.

• When European explorers arrived in Australia, they declared the land as terra nullius, despite the fact that it was already inhabited by Indigenous Australians. This allowed the British to claim ownership of the land and establish colonies.
• In the 19th century, European powers declared parts of Africa as terra nullius, even though the land was already inhabited by various African nations. This led to the colonization and exploitation of Africa by European powers.

These examples illustrate how the term terra nullius has been used to justify the colonization and exploitation of land that is already inhabited by other nations or minorities.