From a few days prior, on April 10th, the opening 2 minutes do a good job of answering the "why" of Bureau of Land Management descending on the Bundy ranch suddenly after 20 years. Basically (according to a real estate broker quoted in the opening 2 minutes) because it's valuable land that the federal government, and wealthy supporters of certain political leaders in Nevada, want to leverage the Bundy family off of, and this is a final push to intimidate them into selling. And that these tactics have worked leveraging out many other family-owned ranches in the area, before this family's tenacity drew a spotlight to the consistent BLM tactics that are used against private citizens.
It also explains the level of support by hundreds of the Bundy family's neighbors.
This Tea Party site shows the same scene unedited, where the BLA officials sic dogs crowd to intimidate them, and throw a 50-year-old woman on the ground. Some of their own words and actions are embarrassing rhetoric, chanting and antagonism, but nothing that justifies what the police did.
This last link gives insight into the written policies of "Environmental Protection", and how it is in truth a mask for locking down control of rural areas, and pushing people into urban areas where people are more easily controlled by an authoritarian state, with less ability to hide, and less able to farm and grow their own food:
