22 people killed and 59 others injured, most of them children.
One of the victims was an eight-year-old girl, who'd gone to the Ariana Grande concert in Manchester, with her mother and sister on Monday night.
This is the second attack in the UK that's been claimed by the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) this year.
Five people were killed on March 22 when British-citizen Khalid Masood drove his car onto the sidewalk along Westminster bridge.
The British government has tightened security and is freeing up nearly 4,000 soldiers to help police, if needed.
The UK also raised its terror alert to the highest level.
But will any of these steps prevent further attacks?
Presenter: Richelle Carey
Guests:
Rizwaan Sabir, Assistant Professor in Criminology at Liverpool John Moores University.
Andreas Krieg, Assistant Professor at the Defence Studies Deptarment at King's College London and a specialist on armed groups.
Oz Hassan, Associate Professor at University of Warwick and a specialist on counter-terrorism.
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