Your armies can move only so much before they must stop and rest. How
much they can move is expressed in the army's move points, and
the move cost of the sectors they must cross.
For example, if an army has 13 move points, and it goes through
sectors with move costs of 4, 3, 2, 2 and 3, it will not have enough
move points left for the last sector (it will have 2 move points left,
and that last sector has a move cost of 3).