without any look on the save, at the moment, i can only guess
are you land mass leader?
i guess not, there is another continent to get
is there room for expansion without war?
i guess not, but maybe there are a few barb cities to capture
do you have several religions in your land?
could be, not sure about it
do you have contact with the other continent?
could be, not sure
can you send troops there?
probably not
are you friends with anyone?
could be, trading partners can be useful
from what i know you could be going for cultural, but i'm assuming you cottage spammed at least 3 cities, and you can spread at least 3 religions.
If this is true, you should grab the whole continent, research until you get cossacks, then switch to 100% (or as high as you can without losing money) culture.
If you got the continent for yourself, cossacks build everywhere, nothing can come to you, short of nukes.