A lot of the towns that have reportedly been captured in Iraq are along the country's borders, allowing Isis to ensure supply routes from Syria, where they already have a presence.
One of them is on the road between Baghdad and Jordan - a country which is home to quite a few Islamic extremists but which is, at the moment, stable.
But if all these towns are indeed falling then pretty much all of Iraq's western border is now in the hands of the jihadists - an extremely worrying prospect for the whole of the region.
All that stands against them now is an Iraqi army which, in the words of one diplomat here in Baghdad, lacks an offensive capability, so is not going to be able to take this territory back.
The Foreign Secretary has been clear on the threat of Isis, but he has ruled out the prospect of any UK military involvement in the crisis.
Iraq’s foreign minister, Hoshyar Zebari, is a natural diplomat. Polite, immaculately dressed, and blessed with a great memory.
Isis has paraded military equipment in Mosul it captured from when the Iraqi army fled in what some see as a "nightmare scenario."