United States Green Cards grant lawful status to the holders. Similarly these cards are granted only to the foreign nationals who seek to live permanently in the United States, forever. Hence, it is mandatory to maintain your primary residence in the United States, as a lawful permanent resident. In order to maintain your primary residence, you must not leave the United States and remain in a foreign country for an extended period of time. Though the United States allows the permanent residents to travel abroad, you need to remember the restrictions. Moreover, you may get into trouble, if you remain abroad for a year or more, without proper documentation.
You will be able to get back to the United States with your Green Card, if you remain abroad for not more than six months but that may not be possible if you reside abroad for a year and more. If you stay in a foreign country for six consecutive months and more, you can get into the United States, only after you prove that you do not have plans to relinquish your status in America. However, you may not get into trouble, if you obtain a re-entry permit before you leave America. This is the best thing that you can do, as a re-entry permit will allow you to remain abroad for less than two years. But you need to obtain this document only if you plan to remain outside America for more than one year and this re-entry permit will allow you to maintain your primary residence in America.
However, you may not be at risk, if you are not absent from the country for six months and more. You need to avoid long unnecessary trips and if you need to remain abroad for a year and more, due to a medical emergency or for some other reason, you may apply for and get a re-entry permit with which you can return to the United States, even if you reside abroad for more than a year. However, you will be permitted to get into the country only after immigration inspection. That is because the US immigration officers believe that a foreign national must hold a US Green Card, only if he wishes to make the United States his permanent home.
However, you may choose to become a US citizen, if you are eligible. That is because US citizens do not have travel restrictions and they may remain abroad for years together. Remember that, you will become eligible for US citizenship only if you maintain your status as a Green Card holder for five years or more. You will have to satisfy few requirements such as continuous residence and physical presence, along with age requirements. You must not have a criminal history and you need to know about the US history and must be well versed in the English language, to apply for US citizenship. However, you can go for US citizenship only if you maintain your lawful status and if you maintain your primary residence in America for five years. Similarly, see to that you pay your taxes, even if you plan to stay abroad temporarily for a year or more. To retain your Green Card, you must not move to a foreign country, intending to make that country your permanent home.