Ammon Bundy's anti-federalism is rooted in religious extremism. He is a fundamentalist Mormon.

This other article is about separate men, but gives some insight into that kind of mindset. It includes a statement from the Church of Latter Day Saints that "strongly condemns" the Bundys' actions.

If anything is clear-cut about Indians in the Constitution, it is that relations with Indian nations are a federal responsibility. Carrying out that responsibility in Oregon, President U.S. Grant established the Malheur Indian Reservation for the Northern Paiute in 1872. It is no coincidence that the historical reservation shares a name with the Malheur National Wildlife Refuge, site of the current armed standoff.

White settlement nibbled at the Maiheur Indian Reservation until the Bannock War in 1878, which ended with surrendered Paiutes and Bannocks on the reservation being removed, officially to the Yakama Reservation in Washington Territory. Unofficially, Paiutes had scattered all over the Western States that comprised their aboriginal lands. The Burns Paiute Reservation is the remains of the Malheur Reservation and the Maiheur Wildlife Refuge is an alternative use for the federal land, for those who believe the federal government exists.

I haven't looked into this. Is Malheur Wildlife Refuge or any of the other disputed federal land part of an Indian reservation?

In 2014, there was a confrontation between the federal government and supporters of Cliven Bundy over the use of federal land near his Nevada ranch. They briefly seized his cattle, then gave them back to avoid violence.

Dwight Hammond Jr. and his son Steve were convicted of federal arson charges for fires they set on federal land in 2001 and 2006. The judge sentenced them to a few months in jail, which they served. The US attorney appealed the sentences, and they were extended to five years, which was supposed to be the mandatory minimum. (This sounds like double jeopardy to me.)

The ranchers marched in protest. Then Saturday night, "dozens" of them, led by Cliven's son Ammon Bundy, seized a building at the Malheur Wildlife Refuge near the Hammond ranch in southeast Oregon. They are demanding the release of the Hammonds, and that the government cede the land to local control.

A lot of people on Twitter are asking why this isn't being called terrorism. (Funny hashtags: #YallQaeda #Yeehawdi #VanillaISIS) No one has been hurt yet, but they are certainly creating great risk of violence, and they have said that they are willing to die.

The Hammonds' hometown of Burns, OR has been tense for a while. The sheriff has received death threats. The residents are not happy about armed men showing up in their town to protest.