LAS VEGAS (Reuters) - Nevada rancher Cliven Bundy and his followers were defying the rule of law by threat of violence, rather than engaging in a legal protest, when they took up arms against federal agents who had seized his cattle, a U.S. prosecutor told jurors on Tuesday.

FILE PHOTO: Rancher Cliven Bundy poses at his home in Bunkerville, Nevada, U.S., April 11, 2014. REUTERS/Jim Urquhart/File Photo

But Bundy’s lawyer countered that the government was at fault for escalating the conflict, and that supporters rallied to his cause because they saw him as the victim of intimidation and excess on the part of federal land managers.

“Why were they there? Because they’re Americans. Because it’s not illegal to help,” defense attorney Bret Whipple said in his opening presentation.

Bundy, two of his sons and a fourth defendant are accused of conspiracy, assault and other charges stemming from the 2014 armed standoff, which galvanized right-wing militia groups challenging U.S. government authority over vast tracts of public lands in the American West.

The revolt was sparked by the court-ordered roundup of Bundy’s cattle by agents of the U.S. Bureau of Land Management (BLM) after he had refused for 20 years to pay the fees required to graze his herds on federal property.

Answering Bundy’s call for help, hundreds of followers - many heavily armed - descended on his ranch near Bunkerville, Nevada, about 75 miles (120 km) northeast of Las Vegas, in April of that year, demanding that his livestock be returned.

Outnumbered law enforcement officers ultimately retreated rather than risk bloodshed, and no shots were ever fired.

The acting U.S. attorney for Nevada, Steven Myhre, laid out the government’s case against the four men in opening statements at a trial expected to last through February, anticipating defense arguments that Bundy and supporters essentially had staged an act of patriotic civil disobedience.

“These events were not protests. A protest sends a message peacefully,” Myhre said. “It is a crime to impede ... an enforcement officer as they execute an order of the court.”

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But Whipple said the U.S. government bore responsibility for stirring tensions to the boiling point, in part by twice taking Bundy to court in the years leading up to the April 2014 showdown.

“The only thing (Bundy) wanted to do was raise cattle, just like his grandfather did, and his dad did,” he told jurors.

During his two-hour opening, Myhre displayed photos from the confrontation showing armed men crouched liked snipers peering through the scopes of rifles he said were pointed at law enforcement.

Whipple played a video clip of a Bundy family member being wrestled to the ground by BLM officers, an image he said was particularly instrumental in winning sympathy for the rancher.

About 20 Bundy supporters formed a prayer circle just outside the federal courthouse in Las Vegas on Tuesday morning. Others packed the defense side of the courtroom gallery during proceedings, many taking notes on legal pads.

Standing trial with Bundy, 71, are his sons, Ammon and Ryan Bundy, along with Ryan Payne, a Montana resident linked by prosecutors to a militia group called Operation Mutual Aid. Each faces 15 criminal counts, the most serious of which carries a maximum sentence of 20 years in prison.

A would-be fifth defendant, internet blogger and radio host Peter Sanitarily Jr., pleaded guilty on Oct. 6 to conspiracy and faces a possible six-year term.

Six lesser-known participants in the Nevada showdown went on trial earlier this year. Two were found guilty, one of whom received a prison term of 68 years. The other awaits sentencing. Two more pleaded guilty to lesser charges in exchange for a maximum one-year prison term.

Yet another group of six defendants, including two other Bundy sons, Dave and Mel Bundy, were due to stand trial after the current trial ends.

One of them, Micah McGuire, 32, pleaded guilty on Tuesday to conspiracy to impede or injure a federal officer. He faces up to six years in prison when sentenced.

Ammon and Ryan Bundy were acquitted last year along with five other people in a separate conspiracy case arising from a six-week armed takeover of a federal wildlife refuge in Oregon in early 2016.