The West has seen Deby as an ally in the fight against Islamist extremist groups, such as Boko Haram and groups linked to Al Qaeda and Islamic State.

ISIS suffered an unprecedented drop in media output since the fall of Raqqa, according to BBC Monitoring. The decline suggests the majority of its media operation was based in its de-facto capital.

The Islamic State began urging supporters to carry out vehicle attacks last year. Europe, where weapons are harder to obtain, has suffered multiple attacks. Now New York has been hit.