Depending on who you ask, Israel or Gaza can be responsible.
Gazan Perspective: It's Israel's Fault
Israel broke the peace treaty and subsequently launched operation 'Cast Lead' a massive military offensive against a civilian population. It banned foreign press from entering Gaza. It used white phosphorus (a chemical weapon) on UN sanctioned hospitals and schools (a war crime). Within 23 days the death toll had reached 1,284 Palestinians dead, 6 IDF by enemy fire and 3 IDF by friendly fire. When the operation had finished Israel had claimed more land from the Gaza strip in the name of security zones for their protection.
Israeli Perspective: It's Hamas' Fault
Hamas failed to control both its own militants and those of the group Islamic Jihad to abide by the terms of the hudna (ceasefire) that they had negotiated with Israel and did not seem interested in renegotiating. They fired large volleys of rockets repeatedly into Israeli territory. After growing Israeli resentment over the attacks, the Israeli government saw fit to use a military incursion to stop the rocket bombardments.
Nobody is fighting against Gaza currently. Israel has previously engaged Gaza militarily in Operation Cast Lead (December 2008-January 2009) and continues to blockade Gaza with Egyptian Coordination.
The Israeli Government launched an attack on Gaza, called Operation Cast Lead, on December 27, 2008. This came after tens of thousands of rockets were launched into Israel during the Israeli-Hamas Armistice or Hudna.
The United States has condemned Hamas' actions and continues to label them a terrorist organization. It endorses, but does not assist in maintaining the blockade of Gaza. However, the Obama Administration did ask Israel to show some restraint during Operation Cast Lead and organized the ceasefire efforts in Operation Pillar Defense.
The war on Gaza started on December 27, 2008.
America is not in any way involved in the Gaza Strip Crisis. The only tangential involvement is that America supports the State of Israel and trades military hardware with them. The United States was diplomatically, militarily, and economically absent from the Gaza Strip and Operation Cast Lead.
Nobody did that, and the Gaza Strip is not part of Israel.
The United States has condemned Hamas' actions and continues to label them a terrorist organization. It endorses, but does not assist in maintaining the blockade of Gaza. However, the Obama Administration did ask Israel to show some restraint during Operation Cast Lead.
Israel attempts to protect herself against terrorist organizations. Gaza is left alone by Israel, except when the terrorists in Gaza attack Israel. For example, today terrorists in Gaza launched over 50 missiles into Israel. When this happens, Israel usually tries to destroy the missile factories.
The war took place all across the Gaza Strip in cities like Gaza, Beit Hanun, and Khan Yunis.
The usual in Israel; Judaism trying to survive, and Islam complaining when Israel doesn't feed the Gaza Strip (they were firing rockets into Israel from the Gaza Strip).
A Hamas Government.Pretty much everything else you can find in Gaza exists in Israel.The reason that Israel is fighting against Gaza has to do with the belligerent attitude and activities of its government. Israel does not want the Gaza Strip to acquire the territory or the people.
The Israelis unilaterally withdrew their settlements from the Gaza Strip in 2005. Israeli military incursions into the region happen occasionally, but the last large Israeli military presence in Gaza was as a result of Operation Cast Lead in late 2008 and early 2009. Israel has not withdrawn in any way from the West Bank.