The Iraqi government's request for help is a reflection of the fact that an army can only be as strong as the country from which it is drawn.
The Iraqi army numbers about a quarter of a million men, it's equipped with all the helicopters and tanks the US gave it - and yet it has folded in recent days and weeks in the face of a few thousand extremist fighters.
There are clear questions about its command and control capabilities and the morale of its troops.
President Barack Obama said tonight that he had urged Iraq's leaders to "set aside sectarian agendas and to come together with a sense of national unity."
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."