At least nine pro-Palestinian activists were killed this weekend in an attempt to break through an Israeli blockade on the Gaza Strip and deliver food, medicine, and building materials to the needy local population. Israel says the organizers of the self-described "Freedom flotilla" were deliberately violating the law and had ignored offers to send aid through proper channels. As the political fallout from the botched military operation continues, here's a look at the blockade that caused the skirmish: 

When was the blockade put in place?

In June 2007, when the militant group Hamas took control of the Gaza Strip after winning local elections. Both Israel and Egypt sealed their borders with the 139-square-mile strip of land, putting tight controls on what gets in and out of the area. The Israeli navy also patrols the coastline.

Why was the blockade initiated?
To prevent Hamas from arming itself, or building weaponry. Rocket attacks from Gaza on surrounding Israeli settlements in September 2007 provoked Israel to declare the strip of land "hostile territory," and tighten its blockade even further. 

How many people does the blockade affect?
Gaza has a population of about 1.5 million.

How much aid gets in?
Israel says it allows around 15,000 tons of humanitarian aid, including food and medicine, into the Gaza Strip each week. But only very basic supplies are permitted: Foodstuffs, hygiene and housekeeping products, animal feed, and an extremely limited set of building materials. The BBC has published a list compiled by humanitarian groups of exactly what goods the Israelis allowed in during 2009 (open PDF). Construction supplies, fuel, metal items, and electronics are all banned as they could potentially be used to create pipe bombs or other types of small arms.

What does the international community say about it?
The U.N. has condemned the blockade. Secretary-General Ban Ki-moon has said it "creates unacceptable suffering, hurts forces of moderation, and empowers extremists." While the U.S. officially supports Israel, President Obama is said to be concerned about the humanitarian crisis in Gaza. 

Why are activists opposed to the blockade?
The extreme sanctions have left Gaza's infrastructure crumbling and its economy in tatters. An estimated 40 percent of Gazans are unemployed, and the U.N. says that 70 percent of local families live on less than a dollar a day per person. Thousands of buildings damaged and destroyed during the Israeli incursion into the Strip in January 2009 still lie in ruins, due to a shortage of building materials. The region has insufficient sewage and water facilities, with the World Health Organization estimating that 80 percent of Gaza drinking water is unsuitable for human consumption.

Why do Israel and Egypt keep it up?
Israel says it will maintain the blockade until Hamas recognizes Israel and pledges to give up its arms. Because it recognizes Gaza as a "hostile territory," it says it is not legally responsible for its welfare, and will only provide supplies necessary to avoid a humanitarian disaster. Egypt says opening the border would represent a recognition of Hamas as a political entity, and undermine Palestinian moderates. (Tuesday morning, Egypt announced it would temporarily lift the blockade to "alleviate the suffering of our Palestinian brothers after the Israeli attack.")

Do people regularly contravene the blockade?
Yes. Until recently, black market goods regularly came into Gaza via a network of tunnels from Rafah, Egypt. However, the Egyptian authorities have recently cracked down on the tunnelling operations and many are now shut. The Free Gaza Movement, whose flotilla is at the center of the weekend's fighting, says it has successfully sailed five boats past the Gaza blockade.

Sources: BBC News, CNN, New York Times, Al Jazeera, AP