Units can be combined into squads.
For example, one unit has 100 health and 50 damage, while another has 120 health and 60 damage.
A squad of ten of the first units has 1000 health and 500 damage, while a squad of ten of the second units has 1200 health and 500 damage.
During an attack, or when one squad attacks another, they simultaneously inflict damage on each other (ranged units do not retaliate).
In this example, during their clash, the first squad loses 600 health, and the second loses 500. Accordingly, the first squad has 4 units remaining with 200 damage, and the second has 6 units remaining with 360 damage. However, if the first squad had the first strike, then after this clash, they would only lose 360 health and would have 7 units remaining with 350 damage.