Defense lines

I'm a little fuzy on the battle mechanic details of what precisely happens when enemy units hit your defense line. for example, if one enemy tank hits a simple defense line shared by two militia, does the tank go up against the combined defense (4+4) of both militia units, so that the computer views the incident as one battle of 8attack vs 8 defense, or does the computer view the attack as two separate battles of 8attack vs 4defence?

They are merged together and they also may get a defence bonus depending on your strategy.

Ok thanks

When you hit a wall made by humans. What do you think happens? Chain effect.

When you hit a wall made by humans. What do you think happens? Chain effect.