We're getting to know just how different ISIS is from al Qaeda

Osama bin Laden's personal letters and day-to-day correspondences -found by US special forces during a 2011 raid on his compound in Abbottabad - reveal a very different approach to waging jihad than that adopted by the Islamic State, an al-Qaeda in Iraq offshoot booted out for its excessive brutality.

There are several similarities between al-Qaeda, starting with their ideological opposition to the West. Both also espouse an extremist narrative, but they differ significantly in their approach to violence, how they choose to capitalize on anti-Western sentiment, and their ultimate aims as terrorist organizations.

Unlike the self-proclaimed Islamic State, al Qaeda - led by bin Laden until his death in 2011 - was never overly concerned with the immediate formation of an Islamic caliphate.

Rather, al Qaeda has always portrayed itself more as a militant group comprised of highly trained operational masterminds whose successful attacks on America and Europe would ultimately gain them enough key followers to form a global movement of Muslims and detain the onslaught of the West.

"You should ask them to avoid insisting on the formation of an Islamic State at the time being, but to work on breaking the power of our main enemy by attacking the American embassies in the African embassies," bin Laden wrote in a letter (presumably) to al Qaeda's future operations chief, Atiyah Abd l-Rahman. "We should stress the importance of timing in establishing the Islamic State."

Educated in the history of Islam and wary of how sectarianism could compromise his vision for an international jihadi movement (or a cohesive Islamic state), bin Laden urged his affiliates to focus on the real enemy, the US, and wage war only on American, Israeli, or European soil.

"Please remind the brothers in Somalia to be compassionate with the people and remind them of the Hadiths on this," bin Laden wrote in 2007 to his operational commander, referring to al Qaeda's blood-thirsty affiliate in Somalia. "Please talk to the Somali brothers about reducing the harm to Muslims at Bakarah Market [in Mogadishu, Somalia]."

The Islamic State - also known as ISIS, ISIL and, to the group's disdain, "daesh" - has adopted virtually the opposite approach to consolidating power across the Middle East and beyond.

Whereas al Qaeda's primary enemy has always been the United States, ISIS targets are much closer to home: Namely, apostate Shi'ite regimes such as Bashar Assad's government in Syria and Haider al-Abadi's in Iraq that impede the creation of a "pure", radically sectarian Islamic state.

The stark contrast between Al Qaeda's large scale, dramatic attacks and ISIS' slow territorial conquest also reflects the differences between the two organizations' ultimate goals: Whereas Osama bin Laden and al Qaeda viewed global jihad as more of a long game, ISIS wants a Muslim state, and it wants it now.

ISIS' mastery of social media and online propaganda has given it the ability to recruit tens of thousands of young jihadists in a way that al Qaeda was never able to do with its written statements and bland, made-for-tv proselytizing.

Daniel Byman and Jennifer Williams said it best in Newsweek: "Which do you think is more likely to attract the attention of an 18-year-old boy dreaming of adventure and glory: a badass video with CGI flames and explosions, or a two-hour lecture on the Koran from a gray-haired old man?"

Al Qaeda cut ties with its Iraqi affiliate, al-Qaeda in Iraq, over worries that AQI's excessive brutality might repel potential followers. Ironically, "the number of converts streaming to aid the Islamic State ... is far greater than in any other modern conflict in the Islamic world," the Washington Post noted earlier this month.

The ideological and strategic differences between al-Qaeda and ISIS are reflected in a 2005 letter from the current leader of al Qaeda Ayman al-Zawahiri to the now-deceased forefather of ISIS, Abu Mus`ab al-Zarqawi, in which Zawahiri urges Zarqawi to foster unity among the Muslim masses in order to further solidify al Qaeda's influence in Iraq.

"If we look at the two short-term goals, which are removing the Americans and establishing an Islamic emirate in Iraq, or a caliphate if possible," Zawahiri writes, "then we will see that the strongest weapon which the mujahedeen enjoy - after the help and granting of success by God - is popular support from the Muslim masses in Iraq, and the surrounding Muslim countries."

"As for the sectarian and chauvinistic factor, it is secondary in importance to outside aggression, and is much weaker than it," Zawahiri continues.

In 2013, Zawahiri sent another letter - this time to the leader of the Islamic State in Iraq, Abu Bakr al-Baghdadi - imploring him to end ISI's ambition to become "ISIL" (Islamic State in Iraq and the Levant) and resolve its dispute with al-Nusra front, al Qaeda's affiliate in Syria.

In a June 2013 speech that cannot be authenticated, but has been widely attributed to al-Baghdadi, the ISI leader rebuked Zawahiri's calls for reconciliation.

His words were foreboding:

"Rise, oh lions of the Islamic State in Iraq and the Levant, and cure the frustration of the believers and attack the hateful Rafidah [Shi'ites], the criminal Nusayris, the Party of Satan [Hezbollah] and those who come from Qum, Najaf and Tehran. Show us from them blood and body parts and tear them apart, for we have known them when we have met them to be cowards."

The Islamic State in Iraq and the Levant remains as long as we have a pulse or an eye that blinks."