In Oligarch, many refugees (such as from Rancagua) were rapidly integrated. However, refugees from a certain conspicuously annoying riverside city coughAvamarcough were systematically discriminated against. Use of the word "Avamar" outside of strategic discussion was prohibited, official policy restricted electoral participation and civic participation, a separate army (message group at the time) was created for them, sent on "special missions" involving significant chance of injury, and systematically underfunded.
It was one of the most fun memories I have of BM: engaging in racial segregation against Avamarians. What does that say about me? Bad things.
On the other hand, Terran welcomed in many Giaskan refugees. We made an official agreement beforehand that they would agree to restrict their political influence and serve in our army (mostly as forward scouts with no units to save gold), in exchange we would fully support their colony under certain conditions. We established statutory delineations of support, including limits to how long we would offer support, and provisions for full integration into Terran if the colony failed. I tried to convert the Giaskans to Triunism, but by and large did not succeed.
