History of Sderot
So, it doesn't look like Sderot was taken as part of a 'defensive' action on the part of Israel.
Sderot, where a few homemade harmless missiles have landed, was once an Arab village called Najd, whose 600 Arab inhabitants were expelled by Israelis in 1948. Jewish settlers built over the old town in 1951. Having been ethnically cleansed, the Arabs moved to the Gaza Strip, along with some other 750,000 Palestinians who had been removed from their lands—or murdered, like the villagers of Deir Yassin—before the first Arab-Israeli war had even begun.
UN Resolution 194 and Article 13 of the UN Declaration of Human Rights say the people of Najd and Palestine’s other 384 demolished villages must be allowed to go home. But they can’t because Israel confines them in a small stretch of coastal desert that the Egyptian army held onto in 1949 and became a dumping ground for the displaced population of southern Palestine. Ninety per cent of Gaza’s 1.5 million people are refugees and their descendants. Israel won’t let them come back, nor will it let them have a state of their own in Gaza and the West Bank even if they relinquish their right of return.