Sentence:  Arrests and prosecutions intensified after Isis captured Mosul in June, but the groundwork had been laid by an earlier amendment to Jordan's anti-terrorism law. It is estimated that 2,000 Jordanians have fought and 250 of them have died in Syria – making them the third largest Arab <WSD>contingent</WSD> in Isis after Saudi Arabians and Tunisians. 
Meaning of the word marked with <WSD> tags:  A quota of troops.