The Israeli-Palestinian conflict is extremely complex and is rooted in the last 60 years of failed policy. However, I think that one of the main causes of the most recent outbreak in violence is the blockade that Israel is placed on Palestine that has made the situation there absolutely horrible. There was a shortage of everything--food, water, medical supplies--even before the Israeli attack started four days ago.
A six month truce between Israel and Palestine that resulted in a severe reduction in violence during that period ended less than a week ago. And now look what is happening. During the truce, Israel still wasn't letting adequate supplies into Gaza.
Is it any wonder that Hamas is shooting rockets at Israel? When people are struggling for the simple necessities of life, they do desperate things.