An Asylum seeker or "refugee" is an individual who was 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. The Unified Earth Government reacted negatively to colonial asylum seekers during the latter years of the Human-Covenant war, interning them in camps when identified as "illegal aliens", along with survivors of glassed colonies such as Coral when their entry visas were refused. Anti-immigration sentiment was present on Earth, with "refuse" being coined as a slang term for refugees.
In the period 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 Ur-Didact's attack on Earth, Fireteam Majestic were tasked with stopping a Sangheili terrorist from detonating a HAVOK Tactical Nuclear Weapon