AS A SHOOTOUT followed by a manhunt paralyzed Boston on Friday, Americans saw on live television how potent even modest terrorist plots can be. Though the facts are still coming in, it appeared that two brothers, perhaps with accomplices, may have carried out Monday’s deadly bombings at the Boston Marathon and then forced the shutdown of the city on Friday as police worked all day to take one of them into custody. If the intention of the alleged bombers, 26-year-old Tamerlan Tsarnaev and his 19-year-old brother, Dzhokhar, was to terrorize and disrupt, they arguably succeeded, despite what appeared to be relatively crude tactics.

At the same time, Friday’s events showed that Americans and their homeland security forces are better prepared to respond to terrorism than they were a decade ago. By collecting videos from surveillance cameras, authorities were able to single out the Tsarnaev brothers in just three days; by releasing images of them, they succeeded in forcing them into the open. On Thursday night, the suspects allegedly hijacked a car and killed a security guard before engaging police in a shootout in which Tamerlan Tsarnaev was killed. Police arrested Dzhokhar Tsarnaev after a standoff on Friday evening. It’s worth recalling that after a bomb exploded at the 1996 Olympics in Atlanta, it was not until months later, and more bomb attacks, that perpetrator Eric Rudolph was identified and not until 2003 that he was apprehended.

It was not clear Friday what motivated the attacks, but there was evidence that the Tsarnaevs, ethnic Chechens who had emigrated with their family from the Russian republic of Dagestan, were admirers of Islamic extremists. A YouTube account in Tamerlan’s name contained videos extolling jihadist ideology associated with al-Qaeda. Sadly, many Chechens have been drawn into jihadist organizations following two brutal invasions by the Russian army, in 1994 and 1999, the second ordered by Vladi­mir Putin. Though Chechen terrorists have mostly targeted Russia, fighters have also appeared in Iraq, Afghanistan, Syria and Pakistan’s tribal territories, and some have joined al-Qaeda.

The Tsarnaev brothers had lived in the United States since 2002 and 2004, so their alleged plot, like that of a number of other domestic militants since 2001, may have been entirely homegrown. Undoubtedly, however, U.S. authorities will seek to learn if the brothers were advised or trained by Chechen extremists, al-Qaeda or another foreign group. NBC reported that Tamerlan traveled to Russia in January 2012 and returned in July.

The FBI and other authorities have disrupted several bombing plots aimed at U.S. cities in recent years. This week’s events in Boston are a sobering reminder that not all such plots can be stopped and that even small attacks can impose relatively high costs. Much as some in Washington might wish it, the war against terrorism is not over.

The Tsarnaevs, however, may have intended more mayhem: They were reportedly carrying more bombs when they were cornered Thursday. That they were stopped so quickly is testament to the effective work of Boston and federal authorities and the cooperation of the people of Boston.