In case there were any doubts, the game has changed in Europe from scattered acts of senseless violence to what appears to be a guerrilla war.

French and Belgian authorities carried out separate raids in their countries that have resulted in the interdiction of a terrorist plot in its "advanced stages," according to French authorities.

It's a good bet that the next few days and weeks will see more arrests.  But they can't arrest everyone involved in terrorism, nor can they stop every plot. 

Fox News:

A 23-year-old resident of the neighborhood described seeing heavily masked and armed officers surround the entrance to an apartment building before entering and emerging with the suspect, his head covered in a scarf.

At the same time,  six people were reported arrested during anti-terror operations in the Brussels suburb of Schaerbeek, the same area where an ISIS flag and a bomb containing nails were found after attacks on the Brussels airport and subway.

Investigators could be seen carrying what appeared to be bags of evidence from at least one of the raid sites.

The raids came as Belgium lowered its terror threat level by one notch although authorities said the situation remained "grave" and another attack was "likely and possible."

There is also word of another plot being planned by the terrorist captured in Belgium last week:

Earlier, the fugitive terrorist suspect who was captured in Brussels just days before a series of coordinated bombings ripped through the Belgian capital on Tuesday – and who claimed he knew nothing of that deadly plot – was reportedly planning a larger, Paris-style attack involving both mass shootings and suicide blasts.

Salah Abdeslam, the lone surviving suspect of the Nov. 13 Paris attacks, denied knowing about the Brussels attacks, which killed at least 31 and wounded at least 270, his lawyer said in court on Thursday. But Abdeslam, who was captured Friday following a four-month manhunt, was set to participate in what could have been an even deadlier massacre, according to Belgian broadcaster VRT.

The plot would reportedly have featured two units of terrorists, one group who would use Kalashnikov rifles to shoot civilians and a second that would blow themselves up in crowded areas. Abdeslam, Mohamed Belkaid, who was killed while shooting at police during a Brussels raid last week, and a third unidentified man were alleged to be the would-be shooters.

That plan is highly reminiscent of the Paris terror attacks, which killed 130. During those attacks, three terrorists blew themselves up outside the Stade de France, while other attackers shot civilians before detonating explosive vests. In the most deadly instance, 89 people were killed after terrorists stormed the Bataclan concert hall during a performance by the American band The Eagles of Death Metal.

Abdeslam is small potatoes.  The truly frightening prospect is that there are bigger fish at large planning an attack that would use chemical weapons, potentially killing hundreds. 

By definition, these cells are relatively small groups of dedicated terrorists – a mix of suicide bombers and trained gunmen.  They are incredibly hard to catch and nearly impossible to stop.  To paraphrase Dick Cheney, authorities have to be successful 100% of the time in heading off a terror attack.  The terrorists have to succeed only once.

With math that daunting, authorities have an uphill fight to stay one step ahead of disaster.