Fifteen years ago, on April 19, 1995, Timothy McVeigh exploded a truck bomb in front of the Murrah Federal Building in Oklahoma City. The explosion killed 168 men, women and children, and wounded hundreds more.
The bombing shocked the nation -- and was a powerful reminder that homegrown terrorism could be just as brutal and hateful as terrorism spawned on foreign shores.
Prior to the bombing, a few watchdog organizations had issued warnings about the dangerous growth of right-wing extremist groups, including the then-new militia movement. In 1994 the Anti-Defamation League issued a report titled, "Armed and Dangerous: Militias Take Aim at the Federal Government" which turned out, unfortunately, to be extremely prescient.
But it took the bombing itself to make most Americans aware of the seriousness of the threat and the potentially violent nature of these groups and their individual members.
McVeigh and his accomplice, Terry Nichols, had an intense hatred of the government stoked by conspiracy theories of government plots to kill the Branch Davidians during their 1993 standoff with the government. Their actions were further inspired by "The Turner Diaries," a fictional blueprint for a white revolution by former neo-Nazi leader William Pierce.
McVeigh and Nichols were hardly alone. From 1995 into the early 2000s, hundreds of anti-government extremists and white supremacists were convicted for a variety of plots, conspiracies and violent acts.
Over the years, though, other serious crises emerged, including the 9/11 terrorist attacks, the wars in Afghanistan and Iraq, the ongoing threat of another attack by Al Qaeda, and a rise in domestic and international Muslim extremism.
The lessons of Oklahoma City, though not forgotten, somehow seemed less urgent in the new millennium.
Those lessons may be more important today than they have been in many years. Over the last 18 months, motivated by factors ranging from the recession to the election of Barack Obama as president, the extreme right in the United States has undergone a startling resurgence.
Anti-government movements such as the militia and the sovereign citizen movements have increased greatly in size and activity. The militia movement alone has quadrupled in size over the past two years, with more than 200 active anti-government militia groups. White supremacist movements, though not experiencing the same increase in size, have demonstrated greatly increased levels of agitation, including calls for violence.
Over the past year, right-wing extremists made headlines through violent acts and plots, including a fatal shooting at the U.S. Holocaust Memorial Museum in Washington, D.C., the deadly ambush of three police officers in Pittsburgh, and the gunning down of a physician in his own church in Kansas, among others.
The arrest of nine members of the anti-government Hutaree Militia, accused of a plot to kill law enforcement officers and their families to create a confrontation with the government that would spark a broader uprising, was just the most recent example of an extremist militia group making headlines.
For experts who monitor the extreme right, the parallels between today and 1995 are disturbing. Extremists have revived the anti-government conspiracy theories that motivated many plots in the 1990s, ranging from alleged "concentration camps" constructed by the Federal Emergency Management Agency to the imminent suspension of the Constitution and imposition of martial law.
Even the Hutaree Militia had ties to militia propagandist Mark "Mark from Michigan" Koernke, the "patriot" leader made infamous during the Oklahoma City investigation after being mistakenly linked to the bombing.
The anti-government sentiments of the Hutaree militia are unfortunately shared by a growing number of domestic extremists, both within and outside the militia movement. The Hutaree arrests are important, but there still exist a growing number of extremists who are already armed and preparing for potential conflict with the government.
Monitoring of Internet chatter related to health care reform and other recent issues indicates that many militia members and anti-government extremists believe this legislation will be followed by the mass legalization of illegal immigrants, postponement or elimination of democratic elections, martial law and gun confiscation. Like the Hutaree, they believe that a "New World Order" of tyrannical rule is coming.
As we remember the victims of the Oklahoma City bombing 15 years ago, and vow that we will never again allow domestic terrorists to strike on our soil, it is essential that our society and law enforcement remains cognizant of the ever-present danger of right-wing extremism in the United States.
Law enforcement agencies should be prepared to apprehend extremists who cross the line from protected speech to illegal actions. Community leaders and elected officials should take this renewed threat of domestic extremism seriously.
The most fitting way to honor the victims of Oklahoma City, and to make sure that their sacrifices were not in vain, is to ensure that no new McVeigh is able to emerge from the shadows to wreak destruction and sorrow.
Abraham H. Foxman is National Director of the Anti-Defamation League and author of "The Deadliest Lies: The Israel Lobby and the Myth of Jewish Control."