I know a Filipina girl who asked a Navy man to marry her so she could come to the US and become a citizen. He was much older than she, but they ended up falling in love and are still married about 15 years later. I studied with her, and she loved learning it all so much. She was an orphan and her mother had studied in the Phillipines, so I think it made her feel close to her.
I had to write a letter for them, when she became a citizen, testifying that it was a real marriage.