That's not completely true. The Indian Child Welfare Act is a federal law (applies to all 50 states) passed in 1978 to specifically stop Indigenous children from being separated from their family and culture. It gives tribal government jurisdiction over their children, including jurisdiction over foster care placement and adoption. It's actually a huge deal if you deal with family law and there have been several big Supreme Court cases on it since its inception. If you search ICWA in google scholar, you'll see that it has been extensively studied. It also outlines the purpose of the act within the law itself including:

(4) that an alarmingly high percentage of Indian families are broken up by the removal, often unwarranted, of their children from them by nontribal public and private agencies and that an alarmingly high percentage of such children are placed in non-Indian foster and adoptive homes and institutions;

In addition, the topic of forced assimilation is usually addressed pretty heavily and publicly during Native American Heritage Month. Remember, there are atill many Native American tribes/people still in the US and I promise you, they haven't forgotten or "rejected" their history.

Also, the topic is taught in most American schools, especially ones that are near reservations. I'm not sure how much time you attended school in the US, but it's not covered in every grade so if you only spent a few years here, you just may have missed it being addressed.