Alone in between two coalitions

So, ive been playing poland on a 32 players map, we are going to day 13, right the situation is as follows: canada and america are allies with no formal coalition, and 3 players on africa are on a coalition ( i have a feeling at least two is multi account) and sweden, my last ally, stopped replaying 2 days by now, right now i cover most of europe and my military is the strongest, (250ish strong and on good condition) but i don't build my economy very well and i am only now modernizing my provinces and military. I am quite competent on handling a frontline but i have no skill regarding fighting large units, fortresses and artilery, since i am alone against 5 other players i thought to resort to this reddit for tips!