In this photo provided by The Daily Free Press and Kenshin Okubo, people react to an explosion at the 2013 Boston Marathon in Boston, Monday, April 15, 2013. Two explosions shattered the euphoria of the Boston Marathon finish line on Monday, sending authorities out on the course to carry off the injured while the stragglers were rerouted away from the smoking site of the blasts.

In all the armchair speculating over who may have detonated the deadly bombs near the finish line of the Boston Marathon this week, the province of Chechnya seldom was heard.

But once it was learned the two brothers who reportedly lobbed explosives at police and engaged in a deadly shootout early Friday had ethnic ties to that region, it opened up a new set of questions and speculations.

As of this writing, about all that can be said with absolute surety is that the world is a dangerous place, sprinkled with people and groups who view their causes and struggles as more important than any regard for innocent lives. Also, that this danger sometimes flares in the United States.

There may be much more to glean soon, of course. Some experts have noted that Chechen separatist forces have ties to terrorist networks, including al Qaida, and that the brothers, Tamerlan and Dzhokhar Tsarnaev, might have been recruited by al Qaida because of their ability to easily blend in and avoid detection in the United States.

But such speculation isn’t worth much. The brothers’ behavior Thursday night and Friday makes it appear they may have been making things up as they went, with no firm plan of escape or funding from abroad — not the hallmarks of foreign operatives.

Meanwhile, a bit historical perspective is important.

Humans tend to view their own situations in a vacuum, devoid of much historical context. They sometimes view current events as signs of new chapters in danger when in fact they are mere continuations of things that have existed a long time.

It is important to understand that organized groups have used terror in this nation to draw attention to themselves since at least the late 19th century. They have gone by various names, such as Fenians, Serb nationalists, Bolsheviks, Dashnaks, fascists, Zionists, Maoists, Guevarists, Black Panthers, ELF and anarchists.

More than a century ago anarchists succeeded in assassinating a U.S. president, William McKinley. For at least two decades they terrorized Americans in a quest to eliminate rulers, clergy and wealthy capitalists.

Someone packed bombs into Gimbel Brothers boxes and mailed them to 36 prominent Americans on May 1, 1919. Only about half reached their targets. The rest were discovered by New York City postal workers. One was addressed to Utah Sen. William H. King. The plot was attributed to followers of the anarchist Luigi Galleani.

Someone bombed Wall Street on Sept. 16, 1920 during the lunch hour, killing about 40 people and injuring many more.

These cases remain unsolved.

Whether the Tsarnaev brothers were a part of this long legacy of terror remains to be seen. They may simply have been part of another long list of disturbed individuals acting on their own, assembling arsenals and carrying out an evil fantasy.

Either way, the events in Boston have been a reminder that the United States, though a remarkably safe place to live, is not immune to the troubles of the world.

Federal and state law enforcement in Massachusetts deserve credit for how they were able to identify and locate these bombing suspects so quickly. They may have kept more innocent people from dying. Tragically, one officer lost his life in the process.

In a dangerous world, public vigilance is imperative. So is an awareness of the world and its history. The United States should never abandon its hard-earned freedoms in the face of such threats, but it must ever be on guard.