Israel, which accepted a cease-fire proposal by Egypt, defended its decision to strike back against Hamas.

"Instead of having this door open to a diplomatic solution, they closed the door," said Mark Regev, spokesman for the Israeli prime minister. "We now have to, unfortunately, protect our people through military means."

While both rockets and rhetoric fly, Human Rights Watch said Israeli air attacks have been "killing civilians in violation of the laws of war."

An Israeli military spokesman said civilian casualties in Gaza are "a human tragedy" -- but that it's Hamas' fault. The military accuses Hamas of taking civilians hostage by using places like houses, hospitals and schools to hide weapons.

More than 200 people have been killed in Gaza since the offensive started a week ago, Palestinian officials said. One Israeli has also died.

Why we should care:

Many credit Israel's Iron Dome for saving untold lives on the Israeli side. In 2014, the United States provided $235 million for Iron Dome research, development and production, according to the Congressional Research Service.

Israel is also the biggest recipient of U.S. foreign aid, much of which has gone toward Israel's military spending.

U.S. Secretary of State John Kerry say's he'll return to the region if a cease-fire doesn't materialize.

"I am prepared to fly back to the region tomorrow, if I have to, or the next day, or the next, in order to pursue the prospects if this doesn't work," Kerry said. "But they deserve, the Egyptians deserve the time and the space to be able to try to make this initiative work."

Chief Palestinian negotiator Saeb Erakat put it bluntly: "We need the United States."

"Now the region is really boiling," he said. "Failure is not an option here."