An impassable barrier is a barrier that is too difficult or impossible to cross. A wall that is impassable is too high or too thick to get through.
When you stake something is to put it in front of or beside you to protect it. You might stake your claim on a piece of land by standing in front of it.
To be disloyal is to be disloyal to your country or to your leader. Someone who is disloyal might go against their government or their leader.
A watchtower is a structure that is used to watch for enemies or for other dangers. They are usually built on top of a hill or a mountain, so that they can see a lot of territory.
When someone defects, they switch their allegiance from one side to the other. This can be a political defection, a religious defection, or a defection in any other kind of war.
To tarnish something is to make it dirty or defective. When you tarnish a reputation, you make it difficult for someone to be trusted or respected.
Pragmatically means in a practical way. When you say that something is pragmatically impossible, you mean that it's not possible in a way that is practical or realistic.
To defuse a situation is to calm it down. When a bomb is about to go off, the bomb squad has to defuse it by removing the detonator.
When two groups of people are reunited, they are finally able to be together again after being separated for a long time.