Operation Pillar of Defence has been expected for months following increasing rocket fire into Israel from Gaza, which a former Israeli army commander described this week as "holding hostage half the population". But the risks of a major operation in the changing Middle East landscape are enormous.
In Gaza, the emergence of militant organisations largely beyond the control of the ruling Hamas make the consequences of Israel's operation unpredictable. Hamas has felt the heat from these ultra-extremist groups, whose members claim that the ruling faction has abandoned military resistance against Israel for the comfort and privileges of a quasi-government.
These jihadist groups have close ties with militants in the Egyptian Sinai, just across Gaza's southern border, which Israel says are driven by an ideology akin to that of al-Qaeda. They are disinclined to listen to Egyptian government mediators, who have brokered a series of ceasefires following escalations of violence. A truce was brokered on Tuesday only to see it shattered a day later when Israel assassinated the top Hamas military commander, Ahmed al-Jabari.
"There are more jihadist groups in Gaza who do not abide by the rules of the game," said retired Brigadier-General Michael Herzog, a former chief of staff in the Israeli ministry of defence. "The Egyptians don't have the same leverage with the jihadists as they do with Hamas."
Threats to peace treaty
Some analysts in Israel have warned that if Hamas was to be toppled in a sustained military operation, such groups could fill a power vacuum, leaving Israel conceivably with an enemy worse than Hamas.
Egypt is another cause for concern. Before its revolution in the spring of 2011, Israel could count on the support of the country's deposed president Hosni Mubarak. But his successor, Mohammed Morsi, who has long ties with the Muslim Brotherhood – Hamas's parent organisation – is likely to vehemently oppose the latest Israeli operation. It could even threaten the 1979 peace treaty between Israel and Egypt.
The offensive against Gaza may also ignite action from Hezbollah in Lebanon. Israel's border with Lebanon has been relatively quiet since the war in 2006, but Israel repeatedly says that Hezbollah has thousands of Iranian-supplied rockets aimed at the Jewish state.
There will also be international condemnation if the Israeli military operation causes widespread civilian casualties in Gaza. In Operation Cast Lead, the 22-day offensive that began in December 2008, about 1400 people were killed in Gaza, including more than 300 children. Thousands of homes and schools were destroyed. Israeli airstrikes are now much more precisely targeted, but civilian casualties are inevitable.
Israel is also going to the polls in January. Most Israeli politicians swiftly endorsed Wednesday's operation, mindful that security is a major factor in all Israeli elections. – © Guardian News & Media 2012