You cross a mountain range at a ‘pass’. It’s the lowest high point on the route. Here they are talking about mountainous Afghanistan. Passes are military significant because land forces have to go over them to advance.

In the subcontinent, a pass is usually a route into someplace through the mountains. I don't recall there being any mountains in Bombay, so it's most likely a route that leads into a city or a town.

In this context pass could mean going through enemy checkpoints and/or gaps between mountains or difficult places to travel through.

I think they mean 'borders', for example: a dividing line between two countries, but obviously on a much smaller scale, so different sections of a town or city.