Qaeda-linked group is now led by hard-liners who are dedicated to global jihad and are putting the region on notice that it could see other similarly spectacular assaults.
"It shows that al Shabab is not an ethnic organization but an ideologically driven outfit and branch of al Qaeda in the Horn of Africa," said Abdirasjid Hashi, deputy director of the Heritage Initiative for Policy Studies, a think tank in Mogadishu, Somalia.
The attack on the Westgate mall in Nairobi — in which gunmen have killed scores of men, women and children — also counters a narrative that al Shabab has been on the wane since UN-backed African peacekeepers had pushed them out of the Somali capital of Mogadishu and major towns in the country since 2011.
"This attack allows the group to reinstate itself as a force to be reckoned with ... and offset reports that the group no longer is relevant," said Natznet Tesfay, head of the Africa country risk team for the IHS business intelligence group.
She suggested the Westgate assault was timed to coincide with the UN General Assembly meeting that began Monday, putting the group at the top of any agenda on African security.
Patrick Smith, editor of Africa Confidential newsletter, called the mall attack "very al Qaeda-esque" and likened it to the 2008 assaults on luxury hotels in Mumbai, India, "sending the message to the rich, the elite, the diplomats that 'You're never safe, we can get to you.'"
Tesfay said al Shabab had launched a campaign to maintain its relevance and credibility following the internal power struggle, which culminated in June with gunbattles in the streets of the southern Somali town of Barawe.
It was fueled, in part, by ideological differences between those who oppose any international intervention in Somalia and want the focus to remain on that internal battle, and those jihadists who believe in a wider conflict linked to al Qaeda's more global agenda.
Somalia has not had a functional government since 1991, when clan warlords overthrew a socialist dictator then turned on each other. al Shabab was established in 2006 and became Somalia's most dangerous militant group, attracting fighters from other countries and carrying out suicide attacks.
It began losing support after a 2011 decision to ban foreign aid organizations from operating in Somalia, leaving millions to suffer in a conflict-induced famine in the country with the world's highest child mortality rate. Tensions also grew between Somali fighters and the hundreds of foreign militants drawn to the impoverished nation.
Four top al Shabab commanders were killed in June, including two co-founders of the group, while its spiritual guide, Sheikh Hassan Dahir Aweys, fled for his life and was captured by Somali forces who have imprisoned him in Mogadishu.
The infighting continues. Earlier this month, an American who joined al Shabab, Alabama native Omar Hammami, was ambushed and killed by rivals in southern Somalia. Hammami had used social network sites to accuse al Shabab leader Ahmed Abdi Godane of being a dictator. He had been on the run since the June assassinations.
Godane, whose nom de guerre is Mukhtar Abu Zubair, appears to be in firm control. It was Abu Zubair who announced in 2012 that al Shabab was allying itself with al Qaeda and who pledged allegiance to the global terror movement.
Emmanuel Kisiangani, a Kenyan-based senior researcher for the African Institute for Security Studies, said the mall attack "speaks about a group that is trying to internationalize its jihad" since "extremist hard-liners mostly trained in places like Afghanistan have succeeded in taking over the leadership."
al Shabab had been warning it would attack Kenya ever since Kenyan troops moved into Somalia in 2011 to take a leadership role in the African peacekeeping force and in pushing al Shabab back into largely rural and impoverished areas, away from lucrative sources of income from illicit taxes and extortion.
In retaliation for Ugandan troops fighting in the African force, al Shabab sent suicide bombers to Kampala, the Ugandan capital, in July 2010, where they killed more than 70 people watching a World Cup final match at two restaurants popular with foreigners. Godane, who has a $7 million bounty on his head, warned at the time that the attack was just the beginning.