Cause and effect
Robert Pape and others have argued that in nearly all cases, terrorism is caused by a (usually valid) grievance. Algerian terrorism against France was caused by French occupation and we know that the London and Madrid bombers were influenced by the invasion and occupation of Afghanistan and Iraq. Such foreign policy blunders are used to recruit people willing to blow themselves and any unfortunate bystanders to pieces.
If the West (read mostly the US and UK) continue to support oppressive regimes and dictators in the Middle East, then they can expect some blowback.
Now please can we bring liquids back on aircraft?