BURNS, Ore. — Surrounded by FBI agents in armored vehicles, the last four occupiers of a national nature preserve surrendered Thursday, and a leader in their movement who organized a 2014 standoff with authorities was criminally charged in federal court.

The holdouts were the last remnants of a larger group that seized the Malheur National Wildlife Refuge nearly six weeks ago, demanding that the government turn over the land to locals and release two ranchers imprisoned for setting fires. For the first time since Jan. 2, the federal land was fully under the control of the U.S. government.

Meanwhile, Cliven Bundy, who was at the center of the 2014 standoff at his ranch in Nevada, was arrested late Wednesday in Portland after encouraging the Oregon occupiers not to give up. Bundy is the father of Ammon Bundy, the jailed leader of the Oregon occupation.

On Thursday, the elder Bundy was charged in the standoff from two years ago. The 69-year-old Bundy was charged with conspiracy, assault on a federal officer, obstruction, weapons charges and other crimes. He’s accused of leading supporters who pointed military-style weapons at federal agents trying to enforce a court order to round up Bundy cattle from federal rangeland.

Federal authorities say the Bundy family has not made payments toward a $1.1 million grazing fee and penalty bill.

The FBI said the final four occupiers were arrested as they walked out of the refuge to the FBI checkpoint. No one was injured and no shots were fired.

Federal authorities were criticized during the occupation for not ending it sooner. But some experts said the FBI’s strategy of letting the tensions die down before moving in ensured there would be no bloodshed.

“This was beautifully executed,” said Brian Levin, a criminal justice professor at California State University, San Bernardino. “This siege and the way it was handled will go down in law enforcement textbooks.”

It was unclear what effect the occupiers’ presence had on the refuge or any of its archaeological artifacts. Videos posted online showed members of the group exploring buildings at the site and criticizing the way tribal artifacts were stored there.