Phillips studies foreign-policy and security issues at the Heritage Foundation, a conservative Washington policy center. He says it has long been known that bin Laden has ambitions to establish a caliphate throughout the Muslim world.
Phillips told RFE/RL that what is intriguing about the letter is that it indicates a division within Al-Qaeda. He points to some analyses that view al-Zawahri's comments as gentle instructions to a loyal subordinate. Phillips says these words must be weighed in the context of al-Zarqawi's position within Al-Qaeda.
"Zarqawi was never part of the core group of Al-Qaeda," Phillips said. "And I think bin Laden and Zawahri essentially brought him in and named him commander of Al-Qaeda in Mesopotamia [Iraq] because they saw him almost as a threat. They knew that he had a better operation there [in Iraq] than they did. But [al-Zarqawi] has never fully subscribed to their ideology."
Phillips noted that al-Zarqawi is an ex-convict from Jordan, a man who lives by violence. He is not like bin Laden and al-Zawahri, who may espouse violence but are also thoughtful, well-educated men.
As a result, Phillips said, al-Zarqawi probably will never be fully integrated into Al-Qaeda. However, he said, this does not mean that he can never lead it.
"He's more like a Mafia-type enforcer who doesn't really see the political niceties that Zawahri does. Implicit in this letter is the political leadership trying to rein in a very brutal lieutenant. I just think that Zarqawi is on the verge of eclipsing Zawahri in terms of charisma, the number of supporters," Phillips said.
Retired U.S. Army Colonel Kenneth Allard agrees it has long been known that Al-Qaeda had a broad political strategy. But the retired intelligence officer says the letter demonstrates the group's ability to adapt -- an asset that he says every successful movement must have.
Allard told RFE/RL that al-Zawahri's instructions to al-Zarqawi show that Al-Qaeda is interested in more than merely killing its opponents -- it also wants to establish a regime that has the broadest possible support among Muslims. He said al-Zawahri's approach to political strategy was enunciated by the Prussian theorist Karl von Clausewitz nearly 200 years ago.
"These guys [Al-Qaeda leaders] are not stupid," Allard said. "What you see there [in the letter] is the apt demonstration that Clausewitz was right all along: [War] is the continuation of politics by other means. What is done tactically has an implication strategically. And you saw a very strong sense there [in the letter] that the senior, [al-Zawahri], was telling the junior, [al-Zarqawi], to make sure that what he was doing made strategic sense -- not to be portrayed as contributing to Muslim-on-Muslim violence."
Allard said Al-Qaeda is a decentralized -- and therefore a very flexible -- organization. U.S. President George W. Bush and Defense Secretary Donald Rumsfeld have acknowledged that fighting Al-Qaeda is unlike any war the Americans have fought before. There are no pitched battles that end with a victor gaining territory.
But Allard said this does not mean that it is futile for Western nations to pursue Al-Qaeda with its military and law-enforcement resources. But it must take the added step of waging a war of ideas. Bush, he said, must do more than merely try to improve America's image in the Muslim world.
The Cold War is a good example, according to Allard. He said the West used its military to help contain the Soviet Union. But he says what ultimately brought victory was the straightforward way in which both U.S. President Ronald Reagan and Pope John Paul II confronted Moscow's ideology.
Allard said the West should do the same with Al-Qaeda. "You have to engage Muslim intellectuals, you have to engage the Muslim street," he said. "So much of what we're doing right now involves talking back. I think in some sense we have got to do a much better job of listening to these people, understanding the basic nature of that criticism and figuring out what we have to do to co-opt it."
And as for Iraq, Allard added, the United States won't defeat the insurgency by killing increasingly more of the enemy, but by killing fewer of them.
For the latest news and analysis on Iraq, see RFE/RL's webpage on "The New Iraq".