Al-Qaeda, means 'the base'. The organisation was set up in 1989 when the Russian Army left Afghanistan.
Many volunteers from Arab countries had gone to Afghanistan during the 1980s. They wanted to help the Afghans fight the invading Russian army.
They supported the Afghans as they were also followers of Islam. For the Arab volunteers the battle was a Jihad or holy war
When the Russian army was defeated al-Qaeda was set up to continue the Jihad against people the volunteers thought were enemies of Islam.
Al-Qaeda now operate in 40 to 50 countries around the world.