Ahmed Jabari, the Hamas chief of staff, was a military man who dedicated his life to war against Israel. His assassination yesterday by the Israel Defense Forces is supposed to send a message to Hamas, to the effect that it would do well to have more moderate figures as its leaders. However, past experience teaches that pinpoint assassinations of the heads of political movements and military organizations are not necessarily effective, and that they usually give rise to even more extreme leaders instead. It suffices to recall Hezbollah leader Sheikh Hassan Nasrallah, who was appointed to his position following the assassination of Sheikh Abbas Musawi in 1992.

The lives of residents of southern Israel became impossible in recent days in the wake of rockets fired from the Gaza Strip. But Israel's chosen reaction - the assassination of a top Hamas official and an attack on Gaza - will only lend international legitimization to continued rocket fire by Hamas. Yesterday evening, rockets were already being fired at Be'er Sheva. And even though the Iron Dome missile-defense system intercepted some of them, the lives of Israeli citizens are being made even harder.

Beyond the fruitlessness of replacing one military leader with another, and of turning the south into a war zone, Jabari's assassination and its timing are liable to turn out to have been a strategic mistake. The escalating violence between Israel and Hamas is likely to make the situation in the entire region deteriorate. The relationship between Israel and Egypt, which is in any case fragile and includes a demonstrative lack of trust between the two leaders, is likely to degenerate rapidly and become a real conflict. A statement by the Egyptian Foreign Ministry yesterday, to the effect that "Israeli escalation will have an impact on the security and stability of the entire region," and the demand of some members of the Egyptian leadership to reexamine the peace agreement with Israel are disturbing signs.

In 2009's Operation Cast Lead in Gaza, Israel acted aggressively, and out of a desire to bring quiet to the Negev towns it harmed many civilians, among them children. Now is the time to remember the lessons of that operation and to avoid, as far as possible, violent actions that will cost the lives of innocent people. Now is the time to act to calm things down.