The day started with a cease-fire, and ended with a ground invasion. Israeli troops moved across the border into the besieged Gaza Strip on Thursday night, the first large-scale ground offensive since a 2008-2009 war that killed more than 1,400 people and caused widespread destruction. The invasion, announced at around 10:30 p.m. local time, followed hours of heavy shelling aimed at clearing improvised explosive devices from the border.