Gaza is a tiny strip of land between Israel and the Mediterranean Sea. It is 45km long and up to 12km wide. It is one of the most densely populated areas on Earth as thousands of refugees fled to the area to escape the fighting in the Arab-Israeli war in 1948 and 1949. Almost 1 million Gazans still live in refugee camps.
Israel has had a lot of control over Gaza since the Six-Day War in 1967. Since then there have been a lot of ceasefires and broken ceasefires. The latest ceasefire was broken by Hamas on December 18, and Israel started bombing Gaza on December 27.
Israel started bombing the Gaza Strip, then sent its troops and tanks into the area. It is hoping to stop the group Hamas from firing rockets.
There are three 'sides' involved. The first is Israel, a country built on previously Arab land after the second world war as a home for Jews.
The second is Hamas, a group the Israelis call terrorists. Hamas is one of two parties in power, and seen by supporters as defending the people and their homeland against the military occupation of Gaza. Hamas has, however, offered truces in return for Israeli withdrawal.
The third group is the people of Gaza. Whether or not they support Hamas, they are trapped, and easy targets for the Israelis. Although Israel says it is not trying to harm civilians, it is impossible to carry out military action without killing and injuring civilians.
Israel has long been financially and morally supported by the United States. With the new president coming in to power on January 20 it may find itself with less support.
Why did Hamas end the ceasefire? Israel destroyed a tunnel that was being dug from Gaza towards its territory.
The destruction of the tunnel also killed six Hamas militants, causing Hamas to say Israel had broken the ceasefire, and attack.
Hamas also has tunnels which spread into Egypt and act as means of trade, they say. But Israel says Hamas uses them to smuggle weapons and has talked Egypt into destroying the tunnels. Almost half the people in the Gaza Strip live below the poverty line. There is no way for them to make money, leading to a severe humanitarian crisis.