How to use A* pathfinding for a large map?

So currently i got used to A* pathfinding and it has been good so far but how do i make the pathfinding on a bigger map with more AI characters(an army for example).
The problem is if i make more graphs that will make the game laggy and same goes to expanding the graph, Also i came to know that multiple AI characters asking for a path at the same time will also make the game laggy. So what should i do to use A*(or another pathfinding system if there is one that is better) on a large map with big number of AI characters???

OKay I found out how to do this, I used the WaypointMaster technique found at unify for when the NPCS are out of sight unless they are visible by the player then they switch to the A* method…

When you are making locomotion programs for a group of entities, it is not practical to do the path analysis for every character, this way you always will end up with something really slow for a game, and will also get unrealistic results as the behavior will be like every entity (or soldier in your case perhaps) will end up looking as if it is acting alone, ignoring everyone else in the group it belongs to.

I don’t think that A* is the way to go ahead with. Have a look here, these are really good works by Craig Reynolds and you can find group/combined behaviors. You can also have a look at Programming Game AI By Example by Matt Buckland, it has a chapter for path planning and briefly deals with group behavior such as cohesion, which I think is a good solution for your question.

I hope this helps!