From Jerome Slater's heavily documented "Just War Moral Philosophy and the 2008–09 Israeli Campaign in Gaza" (pdf):
By 2004 Prime Minister Ariel Sharon had become convinced that the economic and military costs of continuing to defend the settlements were too high—unlike the case of the West Bank and Jerusalem, Israel had little or no religious or nationalist claims on Gaza—so in August 2005 he ordered their withdrawal. Even after the withdrawal, Israel continued to wield overwhelming power over Gaza’s economy and external trade; it maintained control of Gaza’s water, electricity, and telecommunication networks; refused to allow Gaza a functioning airport, seaport, or commercial crossing on its border with Egypt, thus radically cutting Gazan trade and commerce with the outside world; restricted the movement of people and goods in and out of Gaza; prevented farmers from tending to and harvesting their fields and crops; placed severe restrictions on the importation of water for drinking as well as irrigation purposes; and re- served the “right” to launch military incursions at will, periodically bombing and shelling Gaza’s electrical generating system, roads, bridges, farms, and olive orchards. Consequently, even before Cast Lead, the Gazan economy was on the verge of collapse; nearly 95 percent of all factories operating in Gaza had closed down; unemployment ranged from 45 to 60 percent; and 80 percent of Gazans were estimated to be below international poverty lines. Outright starvation was averted by outside assistance, but malnutrition was rampant; the minimal imports of food supplies allowed by Israel were carefully calibrated to prevent a famine, but not more than that.
Read this important article to understand the background of what's going on today. Gaza has has been under Israeli oppression since 1967. One can disapprove of the Gazans' particular tactics (lobbing rockets at civilian areas) while acknowledging that resistance to occupation is legitimate both morally and in international law. When you place people in a desperate position, you can't be surprised when they use any weapons they can get their hands on. The disparity in power and casualties between the Israelis and Gazans (and Palestinians in general) is too obvious to require elaboration.
Slater's paper is also crucial to understanding Israel's long-executed policy of targeting noncombatants and civilian infrastructure, not only Palestinians, but also Egyptians and Lebanese too. When Israel's Labor Party criticized Menachem Begin's Likud government for targeting noncombatants in Lebanon in 1981, Begin responded by documenting similar conduct by Labor governments. No one denied Begin's counterclaim.