Since you're all new to this game, here's why that is a TERRIBLE idea:
As worlds get older and players, bigger, if this was implemented. What stops me from having all of my troops go to one city on an island filled with enemies and then just obliterating them all back to the stone age and then sending them back once done and then sending lots of defenses to that same city so that they all lose everything in their attacks as well??
In a CQest world, that allows players to easily break 99.9% of all sieges, every time, regardless of support
In revolt worlds, this allows players to blow right through support during RR time and land the CS no problem.
All this'll do is cause half the current players, to quit