The following is a theoretical description of the rock-paper-scissors system between troop types and advantage-disadvantage relationships.
Troop wins to:
Infantry blocks cavalry charges; Infantry has an advantage over Cavalry,
Archers shoot infantry; Archers have an advantage over Infantry,
and Cavalry is so fast that they are so difficult to hit, that they are able to charge and reach archers. Cavalry have an advantage over Archers.
Troop Loses to:
Following the above description, Infantry are able to be picked off by archers; Infantry is disadvantaged against Archers,
Archers don't have enough time to aim at fast-moving cavalry, and get run over; Archers are disadvantaged against Cavalry,
Cavalry is disarmed by infantry; Cavalry are disadvantaged against Infantry
and finally, Siege loses to every other kind of troop (as they are not designed to fight against armies, but rather cities).
If 10k infantry attacked 10k archers, the archers would win.