Although there a lot of differences between the US attack on Iraq, and the attack by Israel of the Gaza Strip, there are a number of similarities.
One of which is namely that Israel's November 4th cease-fire violation was just that——a violation; the actions of the Israeli military on November 4th (amongst other acts on other days) did not constitute a necessary act of self-defense.
Israel's military actions in Gaza cannot be justified by the self-defense argument.
Israel's military offensive in Gaza is being perpetrated with enormous disregard for civilian life in violation of fundamental principles of international humanitarian law (IHL). The appallingly high number of civilian deaths and injuries and widespread damage to civilian buildings reflects unlawfully excessive, indiscriminate and disproportionate use of force by Israel.
Two weeks into the Israeli offensive, many international lawyers are raising their voices to condemn Israeli actions from every perspective, challenging Israeli claims to be acting in lawful self-defense. That is, even before examining the unlawful way Israel has deployed its military might, lawyers assessing the self-defense arguments of Israel have found as many holes as in the Gazan ground: Israeli actions were not taken as a last resort, as a necessary response to attacks. Before using force in self-defense a state must need to do so in response to an armed attack, having found no other realistic method of redress or resistance.
In other words, force is only lawful if peaceful attempts to repel the armed attacks either have not worked or would clearly be ineffective. The justification posited by Israel that their objectives of "stopping the rockets being launched from Gaza" and striking Hamas a "severe blow" necessitate the use of overwhelming military force is without legal substance. No force may have been necessary had Israel agreed on 19 December 2008 to open all Gaza's crossings and lift its unlawful siege.
Hamas scrupulously observed the agreed ceasefire until 4 November when Israel launched an unprovoked attack inside the Gaza Strip, killing six persons. Hence the easiest way for Israel to prevent rocket fire would have been to continue to abide by, and then renew the truce it violated on 4 November.