Only crimsons can lead attacks against other cities.
Attack is only possible, if clan has declared war against
other clan and the target can only be city where enemy clans
secret society is.

Cities need war room for handling ongoing wars. In the war
rooms crimson can hire troops(infantry, cavalry, catapults,
etc.) Troops are also needed for the defence of the city.

If city gets conquered its shops are closed for one week
and its citytax is raised by 100% for one month(for the
repairs).

From crimson guild crimsons can occasionally hire specialist
like spys, tactics, officers, clerics etc.

When attack is launched against selected city, you get info
about it in same way you see party status when partying.
Troops which die can be raised/ressed by clerics(only some
of those).

So heres nice little game within game which would certainly
give some interest towards underrated crimson guild. I can
cladly spare more ideas about subject if you want.