a few things happen normally

big countries farm little ones
farmed countries retal big ones
random countries suicide largely big ones
tags go to war

for solo servers it would be relatively simple to implement a system where unless you had personally been attacked by a large country you had a reduced effectiveness that was diminished in line with current c:c dr, ie if your in 90% c:c dr you could have 95% effectiveness instead of 50%

for tagged servers sometimes first strikes are considered overpowered so a situation where damage was reduced by a bit until you started getting hit back might actually be a good thing

that could be an alliance wide diminishing return calculated either purely based on x hits on y tag in z time, or divided by tagged members

and could be a reasonably good benefit for a formal war system if that is ever put in place, so you could declare formal war and eliminate the penalties, either immediately or after a notice period

linking it into a potential restart change where if tag a killed country b, then restart of country b would have no DR against tag a would be fine as well (preferable if restart of b is identifiable as such though)

This is totally epic suggestion actually. That would even remove the need for GDI on express and primary if done harshly enough (its not unreasonable to remove 100% of damage if someone that the target has not hit strikes with missiles).

It would take some work to come up with the formulas that would fit each server though.

Also does it need to be tag based in alliance? I could see this working on individual C:C basis even on alliance with formal declaration (by a tag) removing all penalties but give the defender 24 hour notice and pre-strike chance perhaps.

im a little cautious about anything in alliance that makes clans with certain numbers of members able to get kills and those below just never having enough turns

the advantage of making it tag wide is that any country committing killable quantities of attacks is probably going to die in about the same number of turns

the counter problem to that would be a spy or traitor making attacks deliberately to remove their tags protection, not sure how large a problem that would be though