(CNN) -- Nature abhors a vacuum but terrorism relishes one. And Iraq appears to be offering new space for al Qaeda and other militant groups, as political rivalries and sectarian animosities deepen. The coordinated bomb explosions across Baghdad Thursday -- which killed more than 60 people -- bear the hallmark of Islamic State of Iraq (ISI), which is closely associated with al Qaeda. No other group in Iraq has shown itself capable of such synchronized suicide attacks. Some, but not all, of the bombings were in Shiite neighborhoods; frequently al Qaeda's targets appear indiscriminate as part of a strategy to sow fear and stir sectarian tensions.

But when the U.S. military left Iraq, it took its intelligence-gathering with it -- making the job of
Iraq counter-terrorism units more challenging still.