Actually there was a cease fire until Israel decided not to honour it and attacked Gaza a week before it ended.
18th June:
Israel agrees to ceasefire with Hamas
The ceasefire was to start from June 19th and last for 6 months.
During that "ceasefire", 329 rockets and mortars were fired into Israel.
Following an Israeli incursion on November 4th, in which 6 terrorists were killed, Hamas renewed and intensified their rocket attacks in spite of the
ceasefire agreement. In November there were 190 rocket attacks from Gaza into Southern Israel.
Hamas announced on December 18th 2008 that it would not renew the ceasefire.
GAZA CITY (AFP) — Tension surged in and around Gaza on Friday as the Islamist rulers of the besieged Palestinian enclave declared an end to the
troubled truce with Israel and warned they would respond to any attack.
Source
On the same day three rockets were fired into Israel.
As you see, it was Hamas that ended the cease fire, not Israel. Here is defence minister Barak's response:
Israeli Defence Minister Ehud Barak told the Haaretz newspaper "if the quiet continues, there will be quiet. If the lull is shattered, we will
act."
On 21st December approximately 50 rockets were launched into Israel. The targets included an elementary school and a youth cultural centre.
Israel responded to this by attacking two rocket launch sites.
Then there was a comparative lull, as Hamas withheld rocket attacks at the request of Egypt. That ended on Christmas Eve, when 50 rockets and dozens
of mortars were fired into Israel, hitting homes, a factory, and a playground.
December 27th: Operation Cast Lead begins.
I don't like painting things black and white, good and evil. Societies of human beings are too complex for such simplification, and every action is a
result of an earlier action, and so on and so forth. At some point however we have to draw a line, and for me that line is that Israel is a sovereign
nation with a vibrant democracy and a free press, and has the right to defend its citizens against hostile attacks. And it seems to me that Israel has
historically been remarkably restrained in its response to such attacks.
[edit on 29-6-2009 by mattpryor]