ISIS Advances Efforts

Islamic State militants have accepted a pledge of allegiance by Nigerian-grown Boko Haram extremist group, a spokesman for the Islamic State movement said Thursday.

Boko Haram has been weakened by a multinational force that has dislodged it from a score of northeastern Nigerian towns. But its new Twitter account, increasingly slick and more frequent video messages and a new media arm all were considered signs that the group is now being helped by IS propagandists.

Then on Saturday, Boko Haram leader Abubakar Sheka posted an audio recording online that pledged...

The Islamic State is facing growing dissension among its rank-and-file fighters and struggling to govern towns and villages it has seized, but the militant Sunni group is still managing to launch attacks and expand its ideological reach outside of Iraq and Syria, senior American officials said.

In the seven months since allied warplanes in the American-led air campaign began bombing select Islamic State targets, the Sunni militancy, while marginally weaker, is holding its own, senior defense and intelligence officials said.

Pentagon officials expressed only cautious optimism on Thursday after the...