Stay in US with get green card-how far it good?

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I always heard about US's Green Card.I had apply for it for a long year before.Now many thing happen to US.It make me think how far the US government will keep their promise and serve their new citizen coming with green card to stay with good life?I heard and read that US government and their film also fully with prejudice to people like asian or middle east country....can they proof that they will help us and not only give empty promise?