The Tamil Tigers in Sri Lanka numbered some 50-60,000 men at their height, fighting for a slightly more justifiable cause than Islamic extremism (the end of Sinhalese domination over the Tamil minority) while pioneering many of the terrorist techniques in use today. They were ultimately scattered to the four winds by the Sri Lankan military after a long,brutal war, and yesterday the former Tiger-controlled areas had their first local elections, with a Tamil party coming to power and promising a more peaceful path to equality and autonomy, a result accepted by the national government.
It can be done. The likes of Al-Shabab can be defeated. Not by the intervention of some large foreign power in a conflict (India tried to intervene in Sri Lanka in the 80's and quickly left bruised and bloodied) but by decisive action carried out by regional militaries and governments working together, and more importantly, understanding where groups like this emerge from and fighting them in environments understood by and familiar to the forces on the ground.
It is my belief that the AU and Kenya have done in a few years what seemed impossible a decade ago: forcing the extremist Islamists out of their regional strongholds to the barren plains of Somalia, and finally bringing a ray of peace to Mogadishu after a long, long time (there are ice-cream parlors, movie theaters and TEDx talks there now, unimaginable a few years ago). Al-Shabab has been heavily impaired, and as a result has resorted to attacking a mall in Nairobi to pretend that they're still a threat.
That's my view, anyway. What president Kenyatta must not do now is pull his forces away from their hunt for the remnants of Al-Shabab: that would signal that they have won after all.