Family based immigration is considered to be one of the easiest ways to immigrate to the United States. Many foreign nationals who seek to immigrate to America, feel that they can easily get Green Cards if they get married to US citizens. But that is not so easy as the immigration officers have found that many get married just for immigration purposes. In order to put an end to such fake marriages, USCIS issues only two year Green Cards to the foreign national spouses of US citizens. Those two year conditional Green Cards cannot be renewed and a person who holds such a two year card will have to file Form I-751, at the end of the two year period to remove conditions on that card and to get a 10 year Green Card. But you need to remember that, if you hold a conditional Green Card, you cannot file this petition by yourself and you will have to file this petition jointly with your US citizen spouse and if the petition is not jointly filed, USCIS will not accept your petition.
If you jointly file a petition to remove conditions on your conditional Green Card along with your spouse and if that petition is approved, USCIS will issue you a new ten year Green Card. After residing in the country as Green Card holder for a three year period, you can file Form N-400 for naturalization. Generally, permanent residents will have to wait for five years to apply for US citizenship but spouses of US citizens who have been living in the country as lawful permanent residents for 33 months and who meet all the other prerequisites, may file applications for US citizenship, within three years.
Hence, is it easy to obtain US citizenship by marriage, if your marriage is genuine and if you have not involved in marriage fraud. To apply for US citizenship after residing in the United States for a three year period as a permanent resident, you must still be married to the same US citizen and you must have lived within America continuously for at least 18 months. Likewise, you will have to meet all the other requirements and you must not have a criminal history. If you meet the requirements, you can file Form N-400 and become a US citizen. Remember that, only the permanent residents who obtain their Green Cards through marriage can apply for US citizenship after having their Green Cards for three years and all the other permanent residents will have to wait for five years.