How did Hamas start? Founded in 1987, it owes its creation partly to an Israeli miscalculation. A small Palestinian wing of the Muslim Brotherhood, a religious organisation, was functioning in Gaza, then under Israeli occupation. It was offered financial support by Saudi Arabia to build mosques. Yitzhak Rabin, the defence minister, reluctantly agreed to allow the Saudi money into Gaza, hoping that the new group would counterbalance the feared Fatah force of Yasser Arafat, leader of the Palestine Liberation Organisation. A few months later Hamas was formed during the first Palestinian uprising. Its name stands for Harakat al-Muqawama al-Islamiya, which means Islamic Resistance Movement.

How did it become so powerful? Its initial focus was on social welfare. It created health and welfare centres as well as helping the widows of suicide bombers from 1993 onwards. By the Palestinian uprising of 2000, its mixture of welfare and warfare against Israel had won it popularity and influence. In 2006 it scored a decisive victory in parliamentary elections amid widespread disillusionment with a divided Fatah, its secular rival.

Who leads Hamas? Hamas was founded by Ahmed Yassin, a Muslim cleric who had been in a wheelchair since a playground accident in his youth. Yassin supported suicide bombings and opposed any reconciliation with Israel. In 2004 he was killed by an Israeli helicopter gunship. Abdel Aziz al-Rantissi, his successor, died soon afterwards. Khaled Mashaal, a physics teacher who lives in exile in Damascus, is now the supreme leader. In 1997 Mashaal survived being poisoned by Mossad, the Israeli intelligence agency, in Jordan. Two key figures in a secretive leadership are Ismail Haniya, the former Hamas prime minister, and Mahmoud al-Zahar, a former foreign minister who is believed to have led the offensive against Fatah.

Why the chaos now? Since being democratically elected in 2006, Hamas, which Britain, America and Israel regard as a terrorist organisation, has faced turmoil. Israel withheld tax revenues and Europe its aid. The aim was to pressurise Hamas into renouncing violence and recognising Israel. The result has been widespread poverty, unemployment and growing tension and unrest. Sporadic clashes between Hamas gunmen and Fatah security forces in Gaza have gradually intensified.

Blockade drains life from Gaza

The movement of goods into Gaza had been intermittent at best since Hamas won Palestinian elections early last year

BACKGROUND

• Israel continues Gaza blitz as 310 dead

• Q&A: Hamas and Gaza

• 97 days and counting for BBC's man in Gaza

• Now war is with the enemy within

• The little girl trapped by a quirk of war

What triggered the latest fighting? In an effort to end international isolation, Hamas and Fatah agreed to form a national unity government, but this failed to end friction between their respective gunmen. When fighting broke out again, Hamas fundamentalists saw their chance to seize power in Gaza and drive out the moderate Fatah figures whom they regarded as collaborators for their willingness to talk to Israel.

How big a threat is Hamas to Israel? Hamas has no shortage of fighters and light weapons at its disposal. From Gaza it can bombard Israel with small homemade rockets. Its defeat of Fatah appears to have given it possession of a number of 122mm rockets, the same type that Hezbollah fired into Israel from southern Lebanon last year with devastating consequences. Hamas’s most frightening weapons, however, are the suicide bombers. They have been used repeatedly inside Israel before – and could be used again.

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