If you have items of extreme historical import, can the US Govt. take them away?

Say you find or otherwise come into possession of some some very, very historically significant (to US history) items like critical Revolutionary War documents. Can the US Government stop you from possessing them, or selling them to whomever you please?

Can the US confiscate historically significant items as it chooses or not?

Not if you are entitled to own them.
In other words, if they are not stolen and are legal to own (not a state secret, or a forbidden coin, etc.) then the government can’t legally seize them. There have been recent cases where an individual found one of the original Declarations of Independence, and they were able to do what they wanted with it.

If the items are subject to Native American Graves Protection and Repatriation Act, it is quite possible.

As I discussed towards the end of this thread, the official attempts to film the bombing of Hiroshima and Nagasaki failed and so the only movie footage was taken on cameras issued to crew members by the Los Alamos physicist Harold Agnew. The early pages of this 2005 interview with Agnew has him describing how his assertion of ownership over the originals occasionally came into dispute. Though no doubt both General Groves and, subsequently, Senator Packwood were technically arguing that the films were government property from birth, rather than that they ought to become so simply because of their historical uniqueness. But the latter was clearly a large part of their motivation.
Neither fully succeeded and Agnew eventually donated his material to the Hoover Institute as a suitable non-government home.

(And I may as well take the opportunity to note that my guess in that old thread as to the Nagasaki camaraman was wrong. Lawrence Johnston’s contribution to the book Discovering Alvarez mentions that it was Walter Goodman, also on the Great Artiste with him and Agnew.)

Sure. The government has a right of eminent domain. It can take private property for public use, but it must pay fair compensation. (Normally this is done only with real estate)

I believe that this happened with the Zapruder film of Kennedy’s assassination.

Zapruder gave a couple copies the the Secret Service for free. He sold the original to Life Magazine for $150k which was made in annual $25k payments. He gave the first payment to the widow of J. D. Tippit.

The original Zapruder film was sold to Life Magazine for $150,000. Abe Zapruder did make two copies which he gave voluntarily to the Secret Service.

I’ve never heard of a government in the US using eminent domain for anything other than real property, and I seriously doubt it would be upheld by the courts if their only motivation was historical significance.

The US govt has taken lots of non-real estate under eminent domain. Related to some people I know and their research, a major area of concern are patents. Here’s a link to a NYTimes article from 1912 concerning such a case. Invent a Wonderful Thing and the govt might essentially steal it. (They also have used patented work without paying for it under the claim of “national security”, but that’s another issue. Although is does involve courts being extremely friendly to the govt.)

As one slightly off-topic example, the US Government seized Robert E. Lee’s family property in Arlington, Virginia and turned it into an item of “extreme historical import” by making it into Arlington National Cemetery after the Civil War. Many years later, the Government was ordered to pay compensation to the Lee heirs for the value of the property seized.