Trade, immigration, and political cooperation all have benefits that, when properly applied, greatly outweigh any associated negatives. Goods are exchanged for rare or previously enviable resources, bright minds and manual labor allow for increased productivity, and protection and joint-development flourish. However, sometimes an advanced culture (or a culture that thinks itself advanced) decides that foreigners are a disease and need to be kept away. So the advanced culture cuts itself off from the world. The culture begins a slow decay while neighbors continue to improve. Eventually foreign states look at the once-great backwater and decide the area is ripe for invasion, colonization, or dominance. Imperial China languished because of isolation. North Korea once was industrial while South Korea only had farms. It is possible for countries to recover from isolation, like Japan after the United States opened it up, but it can come at a cost (Japan's rapid rise caused social chaos that allowed for a technocratic military to seize power).
Spaceship Earth-like thinking in geographers
I will scream if I here the term "spaceship earth" uttered by a geographer again if it does not immediately relate to the ecosystem. The theory of spaceship earth states Earth is an enclosed system with a finite amount of resources available to its inhabitants. Further, spaceship earth constricts geographers to studying things from the planet's core to edge of the atmosphere.
The theory ignores outside influence on the planet from the mundane (Sun heats the Earth, Moon's relationship to tides), to worthy of study (Sun's cycles effects on climate), to God-level impacts (Tunguska). It also voids the truth of resources off Earth that can be exploited for future use. Finally, it ties geographers down and closes our minds to geographical studies of the Moon, Mars, and other planets. This is a bold frontier that geologists are exploring without us. We must not be left behind.
Lebensraum-like theories: Homelands are all well and good. But when a culture decides that lesser races are an impediment to progress and must be removed for future growth, bad things happen.
Cultural relativism: "No right, no wrong." Sounds all well and good when studying others but it ignores fundamental values and evolution of one's culture. Is killing homosexuals, anti-female practices, or slavery right? What good is studying the world's problems if one does nothing about them?