@KerrAvon2055 I am not sure this would happen myself. Fortunately, we have never been there. But suppose you had a disease that was not immediately debilitating, but you knew would be fatal, and the country next door were the only people with a cure? The sort of people who stockpiled handwashing during COVID might pack their bags, and take their chances.

I think Churchill wanted to use anthrax towards the very end of the war. The allies had air superiority, so we could do it without fear of significant retaliation. He did not get his way. Germany may have believed we were better at making nerve gas then we actually were.

L'Anse aux Meadows is a Norse temporary settlement in Newfoundland excavated in the 1960s. This was probably used for boat repair, including using bog iron to produce nails. Bog iron is not found in large amounts, and it renews slowly. It is handy when you are far from other sources.

Gold is extracted as a metal. Tin is extracted as an ore. The principle is much the same.

Why are people in the bunker? What are they sheltering from? Can they enlarge their living space, and still retreat to the original steel and concrete bunker in times of need? And where are they getting their materials from? If they are on chalk or sandstone, they may just be able to dig new rooms, or use natural caverns. It could be easy or very hard, depending on the backstory.

If Mars had always been the size size as Earth, it would probably have had a stronger magnetic field, kept its atmosphere and oceans, had moving tectonic plates, and so on. Simple geometry suggests the equator in Mars would be the same temperature as 66 degrees latitude, but the atmosphere would have clouds which would reflect some heat back into space.

@EMS Probably not. Planets condense from clouds of matter. Random collisions will turn kinetic energy into heat, but cannot destroy angular momentum. A cloud of debris will turn into a flat disc, with the particles in nearly circular orbits. These then condense into planets with circular orbits in a common plane.

@EMS No. If the planets have the same length year, they have the same average orbital radius. The nearest I can come up with is some gas giant in the habitable zone, with a set of habitable moons. In this case, the 'year' would by the year of the giant planet.

The most cost-effective part to import might be the dye for the fabrics. A few Kg of ago dyes might be enough to give a small army a unique look. Everything else could be done using native technologies.

@Mon I don't see a problem with water. You might have a shallow sea at the bottom of the valley. The air at the valley edge will be cold and have very little water vapour. If the wind blows along the valley, the cold air would descend, and be very dry. The warm, wet air would drop its moisture as it rose at the other end, giving rivers or glaciers that bring the water back into the valley. Think of the weather in Chile: the winds may blow from the Pacific, but very little moisture makes it to the Atacama desert.