What spurred the armed occupation of a federal wildlife refuge in southeast Oregon

After a two-week trial, Dwight and Steven Hammond were convicted by jury. They were sentenced in October to five years in prison for committing arson on federal land in 2001 and 2006. The pair had been sentenced and served time previously, but on appeal a federal judge ruled that their initial sentences had been too short.
In the 2001 incident, the men, who had leased grazing rights to the land for their cattle, said they had started the fires on their own land to try to prevent the spread of an invasive species of plant, and that the fire had inadvertently burned onto public land. Prosecutors said the fire consumed 139 acres of public land, and was set in an attempt to hide evidence after the men were part of a hunting party that illegally killed several deer on the federal land.
In 2006, the Hammonds allegedly set a “back fire” meant to protect their land after a series of lightning storms had started a fire on the federal property. Prosecutors said that fire then spread onto the federal land.