ISRAEL ESCALATES, GROUND WAR BEGINS…. Israel spent much of the last several days amassing its infantry forces along the Gaza border, in anticipation for a likely ground invasion. Today, that came to pass.

Israeli troops began moving into Gaza on Saturday night, intent on taking out Hamas rocket-launching sites, Israel Defense Forces said.

“We have just a short while ago launched the second stage of the operation against Hamas infrastructure,” IDF spokeswoman Maj. Avital Leibovich told CNN.

“The goal is to try and take over some of those launching areas that were responsible for the many launches — the thousands of launches, in fact — toward the Israeli civilians,” she said.

“What this will do is undermine the peace process,” said Saeb Erakat, chief Palestinian negotiator for the Palestinian Authority, the government of President Mahmoud Abbas.

The move does not come as a surprise. As Leibovich emphasized, Israel dropped leaflets over northern Gaza, signed by the commander of the Israeli military, urging residents to “leave the area immediately” for their own safety. “We are trying to be as humane as possible,” Leibovich said. “… The civilians are not our target. We are looking only at militants, Hamas militants.”

Leibovich added that Israel expects “a lengthy operation,” and Defense Minister Ehud Barak is calling up thousands of reservists as part of the offensive.

Noah Shachtman added, “The week-plus-long air war killed nearly 450, and wounded another 2,050. The house-to-house fighting that lies ahead could be much deadlier.”

It seems unavoidable.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.