Fred Burton of Stratfor has long written on "lone wolf" attacks. This was his first reaction an hour ago to the murder of a policeman and passers by at Westminster.

It's easy for grassroots attackers to conduct simple but effective headline-grabbing attacks using readily available weapons, especially if they are willing to die in the process. The vehicle used here wasn't nearly as large as the ones used in the much deadlier attacks in Nice and Berlin. We've noted vehicle assaults and knife attacks are a simple and effective asymmetrical grassroots tactic. This incident, which got high-profile headlines and disrupted the British capital, will likely inspire similar attacks.

THE EVENT

Four people were killed  (a fifth died later in hospital) — including the attacker and one police officer — and 20 others were injured in a March 22 vehicular assault/knife attack on Westminster Bridge and near the Houses of Parliament.

The early days of ISIL seem far off now. Near three years we have lived with the proto-state that Da'ish/ISIL has come to represent. In 2012 and early 2013, ISIL was a whisper; the mention of an extremist group that was growing in success and riches, gradually spreading its control and taking fighters from other groups. The ink-blot of their control spread out quickly in summer 2013 with their breakneck charge down through the spine of Iraq, culminating in the declaration of the Caliphate. Suddenly, all things seemed possible. Could the group take Baghdad? And could the Caliphate become permanent?

Stopped on the outskirts of Bayji, by the herculean efforts of Iraqi soldiers, the Caliphate stabilised for a while, transforming control of the land and pumping out propaganda on their pure Islamic rule. And the rumours of massacres we heard while they took town after town gradually transformed into the group's trademark slickly edited torture and killings, garnering them international attention that their rule alone never could. All the while, the ink-blot carried on spreading.

Now, under pressure and retreating, with Mosul Airport the latest key area to fall, the analysis of the ISIL's rise and fall in Iraq is beginning.