How Do NASA and other organisations make sure they are at the right spot to pick them up and that the astronauts don’t land in some war zone or remote hard to reach area?
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If you ignore the atmosphere the calculation become very simple. When you slow down the spacecraft to deorbit the trajectory at the opposite side of the planet will be lowered so this is where you will land. Just make sure you are at the opposite side of the planet to where you want to land and you are good to deorbit. With atmosphere the landing spot is not at exactly the opposite side of the planet. But you will have this all calculated as the spacecraft is being designed and there will be tables for how far around the planet you will make it to deorbit. So you make sure to deorbit when your orbit will be over your landing site in the amount of degrees specified in the tables.
But the deorbit burn is not the last time you can normally steer the spacecraft. Capsules have their mass off center so the heat shield on the bottom will form an angled plane to the air in the atmosphere and therefore generate some lift. This allows the astronauts to roll left and right to control their descent and guide themselves towards the desired landing spot.
Even with all this they do not have to land extremely accurately. The recovery crew does have helicopters that can reach the landing site within minutes in most cases. Even if the astronauts had to do emergency landings they have managed to control it close enough to get recovered fairly soon.
There are however some Russian stories of uncommanded emergency landings where the astronauts did not have the luxury of picking a landing site. This was mostly during launch and not in orbit. These have demonstrated that recovery can take days and that the survival training and emergency camping equipment are necessary. Rumor has it that in one of these incidents they did have to cross a country boarder to conduct the recovery and did not ask for permission fearing that they would not be the first on scene, but this is unconfirmed and likely not true.
In general the emergency descent is only conducted when being in a remote wilderness, in the middle of the ocean, or in the middle of a war zone is preferable to being in space a few minutes longer in the current condition of the spaceship.
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