A stack can only move into an adjacent tile, if it passes a command test first. To move the stack the player has to roll equal or less the command value of the character leading the stack. If there is a General with the stack the General will be leading it. Should there be no General the character with the highest command value will lead the stack. There is only one modifier to the command test a -1 for every tile the stack entered this round. Note that is tiles entered and not command tests taken (as you will see there are situations a stack will move through a tile without having to take a command test on leaving the tile).
That the movement on the map and the resulting recruitment possibilities would be "random" was one of the first design decisions. The easiest way would have been to roll a die and move the stack the number of tiles. But to keep it Warmaster like I decided to take command tests. The difference of the nations command values is not very important in this case. For one all Heroes have a command value of 8 regardless of nationality. The different command values of the generals result mostly in a different number of tiles crossed in average. Still there is some advantage because a stack with a command value of 10 is more likely to move at all and being allowed to recruit than a stack with a Ld of 8. Up to now, it did not show to be important.