transCendenZ: At answers.yahoo.com

What made them do it. Not according to me. Citations.
By transCendenZ on http://answers.yahoo.com/question/index?qid=20090105085658AAG8u3U

'Best Answer - Chosen by Asker'
"First Israel is occupying their land for decades now and putting them under siege for a very long time.(the history of the conflict is too long to discuss here)
As for the recent events:
On 19 June 2008, a six-month Egyptian-brokered cease-fire agreement went into effect between Hamas and Israel.

On June 24, 2008 Israel raided Nablus (West Bank) killing two Palestinians, including a commander of Islamic Jihad (an organization independent of Hamas). Later, on the same day, three Qassam rockets were fired into Sderot, Israel, causing two minor injuries. Islamic Jihad, claimed responsibility, stating that this action was in response to the Israeli raid. Hamas subsequently pressured the group into abiding by the ceasefire. On 26 June, rockets were fired by Fatah, a Hamas rival, elements of which sometimes collaborate with Israel.

On 26 June, Hamas warned Israel that its closure of the Gaza border was seen as a major cease-fire violation. Nonetheless, Hamas called on other Palestinian factions to abide by the truce. Rocket and mortar attacks continued, at a rate of several rockets per month, with no one taking responsibility.

On 4 November 2008, Israeli troops raided the Gaza Strip and killed six Hamas gunmen. The Israeli military claimed that the target of the raid was a tunnel that Hamas was planning to use to capture Israeli soldiers. Hamas termed this raid a "massive breach of the truce".

On 13 December 2008, Israel announced that it was in favor of extending the cease-fire, provided Hamas adhered to its conditions. Having previously asserted that an end to the truce would carry huge popular support and that there are daily Israeli attacks, on 20 December Hamas officially announced that they would not be extending the cease-fire, citing Israeli border closures as the primary reason, and resumed its shelling of the western Negev. Hamas blamed Israel for the end of the ceasefire, saying it had not respected its terms, including the lifting of the blockade, under which little more than humanitarian aid has been allowed into Gaza. Israel said it initially began easing the blockade, but resumed it when Hamas failed to fulfill the agreed conditions, including ending all rocket fire and halting weapons smuggling.

Although Israel accuses the Hamas government in Gaza of breaking the truce, the Palestinian Center for Human Rights documented hundreds of truce violations by the Israeli military, including three violations on the very day the truce began on June 19th, 2008".
Source(s):
http://en.wikipedia.org/wiki/2008%E2%80%…

Israel violation of ceasefire on 4th Nov
http://www.guardian.co.uk/world/2008/nov…

graph showing firing rockets
http://atlasshrugs2000.typepad.com/atlas…

Palestinian Center for Human Rights
http://www.pchrgaza.org

Hamas announce end of the truce after repeated Israeli violations (195 violations)
http://www.alsumaria.tv/en/World-News/2-…