Jocko Willink, a retired Navy SEAL and author: “You can’t truly call yourself “peaceful” unless you’re capable of great violence, if you’re not capable of violence you’re not peaceful, you’re harmless.”

We should assume that gravitation is little lower, but pressure of air is a little higher.

So most of the planet is snow and mountains, and only in craters people live. Planets mountains are volcanic in origin and extremely hard - and resist erosion. More importantly they are so cold, that they almost never exposed to liquid water. Mountains are deadly and practically impassable.

There is like 5 huge craters that are not connected. All of them where formed by fragments of metallic asteroid rich with heavy metals. There are some easier routs between some craters, but most are extremely hard.

Snow melts and forms rivers that go to central lakes in craters.

Planet biosphere in the craters is mostly of earth origin - trees, grass, small and large domestic animals, birds, insects and fish.

Most likely planter is result of terraforming and colonization effort - its extremely strange to only large craters that cover planet from all sides and do not intersect, but current population has no idea.

There is no moon, but there are seasons. There is concept on a month, despite not having a moon.

Military ranks and political structure are inspired by united kingdom ship officers.

Ships function in same way as they are in our world - to cross impassable terrain. But in this case it is not sea, but mountains.

Ships fly over mountains performing trade.

Fortresses are built on the edges of craters where it is the easiest to pass.

Fortresses can double as ice mining facilities.

In central lake we can have an island, perfect home for nobility.

Central island may be good place to mine meteorite ore.

Lakes can have deposits of hydrocarbons underneath them.

Religion is one - monotheism. God created people on original planet, an instructed then to live peacefully. But they started a war an destroyed their planet. God said that he doesn't need to punish them they made its own "Hell". But he is loving, and he decided that there are some good people, so he created this planter "Earth" as shelter on the way to planet "Heaven". One day god will retrun and those who sin will be returned back to "hell". Good guys will go to "heaven".

This one section is the weakest one - cultures needs more work

There is this plant called sunflower. I has unique seeds - they as light as air. Plat grows very tall with and releases black seeds when they are ripe.

Around 200 years ago new material was discovered in this seeds - biological aerogel. Agricultural domestication of plant began to produce light and extraordinarily insulating winter cloth for people to cross mountains.

Later was discovered process that allowed to make this material lighter than air - to make large airships that can cross mountain ranges. Old stories say that when such ship crashes, from its carcass sunflowers grow, because some seeds manage to survive process. That is just a story.

Finally recently with advance of chemistry even better purification process was invented - now you can get aerogel than you can pour it on steel frame to form load bearing structure of ship that is lighter that air - material named "Aerolithe".

This sunflower is not actually looks like sunflower, its an alien plant, part of alien flora. That means there is two ecosystems in parallel? Actually not really coexisting. One is quickly driving other one out - alien life forms are almost all extinct. Including sunflower - some of the other part of alien ecosystem is dying out, and this will collapse sunflowers eventually.

So we need two others animals - flying jelly fish one, that feeds on the seeds to actually fly, second one some form of ground worm/bacteria that is necessary for its growth.

Collapsing sunflower yields is the reason for the war.

TODO Countries, society and cultures need more work. Well for sure - arrival, terraforming, living in restricted space should have some cultural side effects! Well well, living in the vertical cities literally gives you a stratification - high, mid and lower classes ) Not that great idea. We do have vertica building in huge cities, and they are not for the poor.