The BBC News website looks at the background to the conflict in Gaza.

Why did the Israelis attack?

The Israelis say they attacked in order to stop the firing of rockets by Palestinian militant groups into Israel. Israel wants all firing to stop and measures to be taken to prevent Hamas from re-arming. It is trying to destroy or reduce Hamas as a fighting force and to capture its stocks of weapons to help achieve this.

The Israeli attack began on 27 December 2008, not long after Hamas had announced that it would not renew a ceasefire that had started in June 2008.

Why did Hamas not renew the ceasefire?

The ceasefire, brokered by the Egyptians, was often broken in practice. There was a vicious circle in which Hamas complained that Israel had imposed an economic blockade on Gaza by land, sea and air and Israel complained that Hamas was smuggling in arms through underground tunnels from Egypt and firing rocket salvos at Israel.

Hamas said it was justified in firing rockets as a method of resistance and to draw attention to the plight of Gazans. Israel said its blockade of Gaza was justified as a means to try to force Hamas to observe the ceasefire.

Events began to come to a climax after the Israelis raided southern Gaza on 4 November 2008 to destroy smuggling tunnels. This led to the further firing of Hamas missiles into Israel and in turn to a much tighter Israel blockade.

Hamas demanded that the blockade be ended or it would not renew the ceasefire, which was running out after an initial six months.

Why does Hamas fire missiles into Israel?

Hamas is an acronym for the Islamic Resistance Movement. It regards the whole of historic Palestine as Islamic land and therefore views the state of Israel as an occupier, though it has offered a 10- year "truce" if Israel withdraws to the lines held before the war of 1967.

It therefore generally justifies any actions against Israel, which has included suicide bombings and rocket attacks, as legitimate resistance.

Specifically in Gaza, it argued that Israel´s blockade justified a counter attack by any means possible.

What casualties have the Hamas rockets caused?

Since 2001, when the rockets were first fired, more than 8,600 have hit southern Israel, nearly 6,000 of them since Israel withdrew from Gaza in August 2005. The rockets have killed 28 people and injured hundreds more. In the Israeli town of Sderot near Gaza, 90% of residents have had a missile exploding in their street or an adjacent one.

The range of the missiles is increasing. The Qassam rocket (named after a Palestinian leader in the 1930s) has a range of about 10km (6 miles) but more advanced missiles, including versions of the old Soviet Grad or Katyusha, possible smuggled in, have recently hit the Israeli city of Beersheba, 40km (25 miles) from Gaza and brought 800,000 Israelis into range.

Palestinian medical sources say that about 700 people have been killed in Gaza during Israel´s current campaign there.

What have been the effects of the Israeli blockade?

They have been severe. Economic activity was already at a low level when the Israeli attack began. The United Nations Works and Relief agency (Unwra) provides basic food aid to about 750,000 people in Gaza. The director John Ging said when the blockade tightened in November that Unwra was running out of food.

Since the Israeli attacks began, Israel has said that humanitarian supplies will be allowed in but the level of supply has been less than it used to be. There have also been shortages of fuel and medicine.

What is the history of this small strip of land?

Gaza was part of Palestine when it was administered by Britain in a mandate granted by the League of Nations after World War I. In fighting after Israel declared its independence in large areas of Palestine in 1948, the Egyptians captured the Gaza Strip. Palestinian refugees from the coastal cities to the north took refuge there. They or their descendants still live in UN camps in Gaza. Israel captured it in the war of 1967 and eventually moved about 8,000 settlers there, but all Israeli settlers and soldiers left in 2005.

Gaza has a population of 1.5 million of whom some 33% (about 490,000) are classified as refugees. It is 40km (25 miles) long and between six and 12km (4 and 8 miles) wide.

How did Hamas come to control Gaza?

After the Israeli evacuation in August 2005, the Palestinian Authority took control of Gaza. The PA was made up mainly of secular- minded Palestinian nationalists from the Fatah party, which, unlike Hamas, thinks that a final agreement with Israel for a two-state solution - Israel and Palestine - can be made.

In January 2006, Hamas won elections to the Palestinian legislature and formed a government in Gaza and the Palestinian territories on the West Bank. A unity government between Hamas and Fatah was then formed in March 2007 but the Palestinian Authority President Mahmoud Abbas, a Fatah leader directly elected in an earlier vote, subsequently dissolved the government.

In June 2007, Hamas, claiming that Fatah forces were trying to launch a coup, took control of Gaza by force, but not the West Bank territories.

Hamas was boycotted by the international community, which demands that it renounce violence and recognise Israel.

How might this end?

Diplomats hope there can be a new ceasefire agreement. This would have to be based on three principles. Two of these are demanded by Israel - a commitment by Hamas not to fire rockets into Israel, and a method (perhaps some kind of physical barrier) to stop the smuggling of arms. One is demanded by Hamas (apart from the withdrawal of Israeli forces of course) - the relaxation of the blockade on Gaza.

If there is no agreement, Israel will try to impose its conditions by force. Hamas will contest it. (© BBC MMVIIII 01/08/09)