The almost 20 months of war has torn Gaza apart, often displacing residents multiple times and killing more than 54,000 people, according to the Hamas-run Health Ministry. A U.S.-brokered ceasefire agreed in January collapsed in March as Israel enforced a blockade on all humanitarian aid into the strip.

Former U.S. Ambassador to Israel Michael Oren joins "Elizabeth Vargas Reports" to discuss Greta Thunberg's attempts to sail to Gaza and Israel's response that it will block her from reaching the embattled area.