[saybanana]

Secondary immigration is what drives up immigration from Asian countries.
Immigrants get visas/green card, become citizens over time. Then they can sponsor green cards for their family members.
Spouse/children (child/adults)
Parents
Siblings and their family

Then the cycle starts again where once they become citizens, they can sponsor their family. So a Brother in Law , married to your sister can sponsor his parents and siblings.

Strong economic countries where the people are near economically equal with the US like Japan, Singapore for example (maybe south korea), will less likely send as many people to the US thus having lesser secondary immigration.

Poorer and developing countries will likely have higher secondary immigrants as a way to escape poverty and have better chances in life for themselves and their entire generational family.