Bashar al-Assad’s military used cluster bombs against a civilian town earlier this month, a move that activists said on Friday could serve as a tipping point. The attack on Marea on December 12 killed 4 civilians and injured 23 others. The use of cluster munitions is banned by much of the world, but it is consistent with Assad’s slow escalation of weapons throughout the year. After starting with mortars and tanks, Assad began using cluster bombs against rebel forces over the summer. Just this month, the government started launching cruise missiles with conventional warheads. Analysts say he used this “boil-the-frog-slowly” strategy to prevent Western intervention.