From Halopedia, the Halo wiki
An asylum seeker or refugee is an individual who has been displaced from his or her home region due to war and violence; famine or out of fear of persecution, and seeks to live in a foreign nation. During the Human-Covenant War, colonial refugees seeking asylum on Earth were often referred to with the derogatory term refu. The plural word is "refues", a homophone of "refuse," used to imply that such people are garbage.
Many people from the Inner Colonies who began fleeing to Earth after the Outer Colonies fell to the Covenant during the Human-Covenant War. Complying with its standard immigration laws, the Unified Earth Government reacted negatively to colonial asylum seekers. With the ever-present threat of being the next colony to be glassed, people from worlds like Coral gained entry to Earth, being forced into refugee camps. Sophia Bossedon used underground connections to get an illegitimately-earned visa in order to avoid being caught and sent back. When such "illegal aliens" were forced to suffer the realization that their homeworld had finally been destroyed in 2552, Earth continued to intern these people despite there no longer being anywhere to return them to; Sophia was caught up with the post-Coral internment. Some human colonies, like Chi Rho, became home to thousands of refugees.
In the years immediately after the Human-Covenant War, refugees from the former Covenant member and client races sought asylum on Earth, leading to the South American city of Rio de Janeiro becoming a hotspot for migration (whether it has been outfitted for such an event, or is simply a popular destination is uncertain). Not all asylum seekers migrate to a host country for legitimate means; at the time of the Didact's attack on Earth, Spartan elements were tasked with stopping a Sangheili terrorist from detonating a HAVOK tactical nuclear weapon.
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