Momentum that has swept Syrian rebels to a series of swift victories over President Bashar al-Assad appears to have slowed in two major attacks aimed at capturing the cities of Aleppo in the north and Deraa in the south.

The reasons include a determined military effort by the government and its foreign allies to stem the tide of setbacks, and shortcomings in rebel strategy and weaponry that have made it harder for them to capture two cities of strategic value.

This does not necessarily mean Assad, his sway mostly confined to western Syria, is on the cusp of a major fightback. The army and allied militia remain overstretched in a multi-sided war pitting them against Islamic State, al Qaeda, and more moderate rebels. […]