United States
1.) Automatic Birthright citizenship.
2.) Green card lottery. (give citizens of certain countries a chance to win a Green Card)
3.) Siblings can file for foreign siblings to enter America. (Example~ Your British brother marries an American and goes on to get American citizenship. He now can file to bring his Siblings to America)
4.) Parents can file to bring adult children to America. (Example~ Your British mother marries an American and goes on to become an American. she now can file to bring her adult kids to America)
5.) Children over 21 can file for their parent's.
Vs.
United Kingdom
1.) Ban Automatic Birthright citizenship in 1983.
2.) Got nothing like the United States Green Card lottery.
3.) Siblings can’t file for foreign siblings to enter the United Kingdom. (Example~ my brother marries a British citizen and goes on to get British citizenship. He can’t file to bring me to the UK)
4.) Parents can’t file to bring their adult children to the United Kingdom. (Example~ my mother marries a British citizen and goes on to become a British citizen. she can’t file to bring her adult kids to the UK)
5.) It’s rare that the British government allow Children to bring their foreign parents to the UK.

