As I write the Commons is about to debate and vote on military action against ISIL in Syria.
France, our neighbour and one of our closest allies, has asked for our help. Its Foreign Minister has said: "we need British defence capabilities to win this war".
If ISIL attacked Britain, we would expect the same support from France. Terrorism and Islamist extremism clearly threaten us. We need to stand together to confront it.
ISIL thrived while the world ignored it. But competent local ground troops, supported by Western air power, have been able to drive it back and recover the territory it has seized.
We are already engaged in air strikes against ISIL in Iraq. It makes little sense that our pilots cannot cross the border into Syria when our allies can.
It's said that we are now changing sides: that initially we wanted to attack Assad, but now we want to attack his enemy, ISIL. We need to deal with both.
The world's failure to confront Assad, who has killed hundreds of thousands of his own citizens and displaced millions of others, has accelerated the rise of ISIL who many Syrians saw as the only body fighting him.
Military action must be part of a wider strategy to eliminate ISIL and begin a peace process in Syria which sees Assad stand down. But peace requires ISIL to be beaten back.
It is argued that, after the Iraq War and action in Afghanistan and Libya, intervention can never be successful. But we must learn from the mistakes following military action, not make the far bigger mistake of ignoring those who slaughter their own citizens or threaten us.
ISIL's extremism has inflicted unimaginable cruelty on Syrian and Iraqi citizens: punishment cages in town squares; the execution of women they consider too old to be sold as sex slaves; gay men thrown from buildings.
To those who say this isn't our war, I ask them to remember the attack on Paris. The waves of desperate refugees from Syria who are arriving at Europe's border also show that we cannot insulate ourselves from what is happening in the Middle East.
For all these reasons, I will certainly vote for military action.