A massive Israeli offensive against Hamas in the Gaza Strip has left 47 dead over two days, as tensions between Israel and the Palestinian militant group reach a tipping point.

The Israeli government has authorized the military to call up 40,000 reservists as it prepares for what the country's defence minister has warned would be a long-term offensive.

Meanwhile, militants in the Gaza Strip have unleashed more than 160 rockets at Israel, including one that managed to reach the northern Israeli city of Hadera, located about 100 kilometres from Gaza.

Israeli foreign ministry spokesperson Paul Hirschon said between 600 and 700 rockets and missiles have been fired "indiscriminately" into Israel since the beginning of the year – about half of which have been fired in the last three weeks.

"It's one thing to get them to stop firing rockets and missiles," he told CTV News Channel on Wednesday. "It's another thing to get them to stop firing rockets and missiles for a long time."

CTVNews.ca looks at the events that led to the latest Israeli-Hamas conflict to determine why it has escalated so quickly.

May 2014: Israeli teen murdered in taxi, Israeli-Arab charged

In early May, 19-year-old Shelly Dadon was stabbed to death during a taxi ride. The murder was followed by protests, which called for Israel to end the practice of prisoner exchange.

The Israel Security Agency later charged an Israeli-Arab taxi driver in the murder.

June 2014: Missing Israeli teens found dead in West Bank

Three teens-- Eyal Yifrah, 19, Gilad Shaar, 16, and Naftali Fraenkel, 16, -- disappeared on June 12 while hitchhiking from Jewish seminaries in the West Bank. Israel blamed Hamas for the abductions, without providing evidence, and launched a widespread crackdown on the group. Hundreds of Palestinians were arrested while Israeli security forces conducted a feverish manhunt for the missing youths. A 13-year-old Palestinian boy was killed by Israeli soldiers during the raids.

About two weeks after they went missing, the teens’ bodies were found in the West Bank. Israeli Prime Minister Benjamin Netanyahu blamed Hamas for the murders and said the militant group "will pay."

Hamas denied any role in planning or carrying out the killings.

July 2014: Arab teen abducted, killed in east Jerusalem

On the same day the Israeli teens were buried, 17-year-old Mohammed Abu Khdeir was abducted in east Jerusalem and burned to death. Three Israeli suspects later confessed to the crime, which police described as "nationalistic."

Officials reported the confessions as Palestinian militants bombarded Israel with some 40 rockets and mortars, drawing Israeli airstrikes in retaliation. At least 8 Palestinian militants were killed.

July 2014: Beating of Palestinian-American boy caught on video

A video posted online appears to show Israeli police officers beating 15-year-old Palestinian-American Tariq Khdeir who was arrested during protests in East Jerusalem. The protests followed the death of Mohammed Abu Khdeir, Tariq Khdeir's cousin. Khdeir was accused of attacking security officers and rioting, which he denied.

July 2014: Hamas fires rockets into Israel, Israel responds

The murder of Mohammed Abu Khdeir, beating of Tariq Khdeir and the clamp-down on West Bank during the search for the missing Israeli teens left Palestinians furious and led to riots in Jerusalem, the West Bank and some Israeli-Arab towns.

On Monday, Hamas fired rockets into Israel, which Israeli responded to by launching strikes in Gaza.