National security expert Dr. Sebastian Gorka said that Monday's attack on a Christmas market in Berlin, Germany represented "the sad reality" of the fight against terrorism.

"There is no front line like there was in World War I and World War II," Gorka told Eric Bolling on "Hannity" Monday night. "The front line is when you leave your house in the morning or when you go to a Christmas market in downtown Berlin."

SUSPECT IN BERLIN CHRISTMAS MARKET ATTACK REPORTEDLY CAME TO GERMANY AS A REFUGEE

Gorka added that ISIS had "learned from the mistakes of Al Qaeda," making them more dangerous than Usama bin Laden's jihadis.

"Al Qaeda was, ironically, too successful on Sept. 11. They killed 3,000 people in 102 minutes. So afterward ... they wanted to go bigger and bigger and bigger," Gorka said. "ISIS understands this is just about guerilla warfare. They’ve said, ‘You don’t need to build a bomb, you don’t even need to get a gun. Get in a truck and' — literally, they wrote — 'mow the infidel down like grass.'"

Gorka said that the key to preventing or surviving terror attacks like those in Berlin or in Nice, France on Bastille Day of this year was to be "tactically aware."

AT LEAST 12 DEAD, 48 INJURED AFTER TRUCK PLOWS INTO BERLIN CHRISTMAS MARKET IN APPARENT TERROR ATTACK

"Look at downtown centers or any suburb, and people are walking around staring at their iPhone or their Android," Gorka said. "Well, you know what? Then you are a target. You’ve got to be aware of your surroundings.

"So, people need to – as the police say, your head should be on a swivel and you should be tactically aware every time you leave the house in the morning."