Mirai Shounen Conan Japan

In July 2008, nations use magnetic weapons... probably based on Tesla's work or scalar technology, to start a world war with cataclysmic consequences. The continents sink into the oceans like Atlantis did and survivors attempt to escape the rampaging planet on spaceships. Lacking sufficient thrust, the gravity of terra firma reels the ships back in and many crash into the oceans. Some make it back intact and a sliver of humanity clings to survival in the aftermath.