If Afghanistan provided combat training for Al-Qaeda jehadists nearly three decades ago, Iraq since the US-led invasion has become the main front in the network's holy war and provided a breeding ground for more converts to its violent ideology.
"In the last three years, Iraq has become a generator of terror cells for Al-Qaeda. Thus, the US war on terror, of which the Iraq war was supposed to be part of, has grown to be the main source of terrorism," says Amr al-Shawbaki, an expert on Islamic jehadists movements at Egypt's al-Ahram Centre for Strategic Studies.
The Iraq war, widely perceived by Muslims as a war on Islam, has given strength to Al-Qaeda's ideology.
Thousands of Muslims, who in the past might have been silent Al-Qaeda sympathisers, are now embracing its ideas of a universal holy war on the West and its puppet regimes in the Middle East, analysts say.
"For Al-Qaeda itself, Iraq has provided a substantial boost in support. It has been possible to represent the conflict as an American neo-Christian occupation of a key Arab state," argues Paul Rogers, a global security expert from the Oxford Research Group.
Al-Qaeda supporters are using the propaganda value of the Iraq war to justify terrorist attacks launched across the world as long as the occupation of Iraq continues.
The Madrid train bombings in March 2004 and the attacks on the London transport system in 2005 were carried out in retaliation against the Iraq invasion, the attack perpetrators and many Muslims maintained. But this view was vehemently contested by the Spanish and British governments.
Thousands of foreign combatants, mostly Arab nationals, have been crossing into Iraq, especially via neighbouring Syria, to take part in the holy war, often under an Al-Qaeda banner.
Nevertheless, homegrown Iraqi insurgents make up the majority of Al-Qaeda followers in Iraq, which under its former regime was much less hospitable to the terrorist network than it is now.
Jehadist activity, analysts think, has become noticeably concentrated in Iraq and decreasing across the world since the London bombings on July 7 2005 and the attacks on hotels in the Egyptian tourist resort of Sharm el-Sheikh 16 days later, both of which were blamed on Al- Qaeda sympathisers.
The network has become diffuse. With limited links to its leader, Osama bin Laden, loosely connected local groups are embracing his highly infectious ideology and carrying out on their own initiatives in the onslaught on the "infidels".
"After the 9/11 attacks, Al-Qaeda has entered another stage, evolving into terror cells without an organizational framework to connect their members," al-Shawbaki says.
"Its cells have spread just in the same way McDonald's is present everywhere in the world. Through franchises," he argues.
The emergence of the Jordanian fighter, Abu-Musab al-Zarqawi, in Iraq, is a good example of a terror cell identifying with, but not directly connected, to Al-Qaeda's central command. Al-Zarqawi built his own parallel Al-Qaeda in Iraq group, which he commanded until he was killed in a US air strike on his hideout in June 2006.
Al-Qaeda gained its first cadres of loyalists in Afghanistan where they acquired combat experience in their holy war against forces of the former Soviet Union in the 1980s. But the combat training, which the new generation of loyalists is gaining in Iraq, is superior to that of Afghanistan, analysts think.
It is training against "the world's most heavily armed and best-equipped forces, the US Army and Marine Corps supported by the US Air Force and Navy," Rogers opines.
State-of-the-art weapons are used by the US army from the latest light arms, precision-guided munitions to mortar-detection radar systems and aerial and satellite-based reconnaissance.
The confrontation in Iraq is mainly an urban guerrilla war, argues Rogers, and is therefore similar to the kind of conflicts, which Al-Qaeda will want to launch against other regimes in the Middle East.
This is why the network is likely to want the Iraq insurgency and US occupation to continue, which will add more loyalists to its ranks.
A large number of supporters are needed by Al-Qaeda to achieve its long-term objective of toppling the region's corrupt regimes and the establishment of true Islamic rule.
For Al-Qaeda, Iraq is becoming "not so much the immediate core focus of a war against Western and local elites, but much more of a means of developing the paramilitary forces to enhance a decades-long conflict", says Rogers.