Hundreds of thousands of Gaza residents sought to heed Israel’s order to evacuate roughly the northern half of the territory, while others huddled at hospitals in the north on Sunday. Gaza’s 2.3 million civilians faced a deepening struggle for food, water and safety, and braced for a looming invasion more than a week after Hamas militants launched a deadly assault on Israel. Israeli forces, supported by a growing deployment of U.S. warships in the region, positioned themselves along Gaza’s border and drilled for what Israel said would be a campaign by air, land and sea to dismantle the militant group.