On paper, H1B is a temporary worker program that requires non-immigrant intent. In practice, there is a legal fiction called “dual intent” that allows H1Bs to apply for a green card without violating the requirement of non-immigrant intent. Once a permanent resident, they can sponsor spouses and adult children for permanent residency. Once a citizen, they can sponsor parents and siblings.
The U.S. gave my dad an H1 visa, which resulted in 8 other Bangladeshis moving to the U.S. If my mom wasn’t antisocial, she could’ve sponsored her dozen siblings, who could’ve then sponsored their children. That’s how you end up with ethnic enclaves like Little Bangladesh.
Let's be a bit clear on the timelines though. Right now if you get an H1B to the US (good luck), it's 10+ years before you could get citizenship, and that's assuming your employer sponsors you and you get an EB- green card. You could then bring your parents within a few years, but it would be like another 15+ year wait to get your siblings in on an F-4 visa.
So it's not like folks are getting an H1B and then shipping over their entire families on the next boat, it's decades depending on their relationship to you.
10-15 years isn’t a long time on a social timescale. It’s actually very quick. That means a small number of H1B immigrants can give rise to a large immigrant community within a few decades, as has happened with Bangladeshi enclaves around the country.
The U.S. gave my dad an H1 visa, which resulted in 8 other Bangladeshis moving to the U.S. If my mom wasn’t antisocial, she could’ve sponsored her dozen siblings, who could’ve then sponsored their children. That’s how you end up with ethnic enclaves like Little Bangladesh.