Foreign nationals who get married to US citizens will be granted US Green Cards and this is the easiest way to get Green Cards in the United States. That is the reason why people who wish to settle in the United States get married to US citizens solely for immigration purposes. But to get a Green Card by marriage, you must be legally married and your marriage must not be a marriage of convenience and people who involve in marriage fraud will be penalized and removed from the country. However, in most cases, USCIS grants two year Green Cards to the spouses of US citizens, in order to combat marriage fraud. These two year Green Cards are not renewable and the people who hold these two year cards will have to file petitions to remove conditions on their cards and to get new ten year Green Cards.
Nevertheless, US citizens who get married to citizens of foreign countries can file petitions for Green Cards for their spouses. If the US citizen spouses file immigrant petitions, Form I-130, for their spouses who are non US citizens, while they are in their home countries, they will become eligible for immigrant visas, after the approval of the immigrant petitions filed by their US citizen spouses. In this case, they can travel to America with those visas and live there with their US citizen spouses and their Green Cards will be mailed to them. If the foreign national spouses are in the United States and if their US citizen spouses file Form I-130 for them, they need not wait until those immigrant petitions are approved and they can apply for adjustment of status on Form I-485 and to file this form they need not return to their native countries and they can do this while in America. This adjustment of status process will allow the foreign national spouses to adjust their status and obtain Green Cards by marriage, while in America.
Generally, people who apply for immigrant visas will be put on waiting lists and they will be granted visas only after their priority dates become current but this does not apply to the spouses of US citizens and there is no limit in the number of Green Cards that are issued to the spouses of US citizens. This process sounds easy, but people who got married to US citizens recently and people have not been married for two years, will be issued only two year Green Cards, with conditions. In this case, they must wait for two years and file petitions to remove conditions and apply for and get Green Cards valid for ten years, at the end of the two year period.