During the period of environmental and economic instability that challenged most of Earth's peoples during the 21st century, many saw the continuance of living under such circumstances as untenable. Low-intensity conflicts plagued even the most advanced of nation-states. Because of the degradation of the ozone layer, numerous cancers were on the rise. Some held out hope for interplanetary colonization as a means to start over. Others were concerned that the extant ideological, ethnic and racial conflicts would only be transplanted to other worlds.