Just some short tipps:
- Play on very easy mode
- Play 100-150 rounds as best as you can
-- Take many one-region-countries
-- invest as much as you can
-- always sell your propperties until you have enough cash that it won't bother you when something gets blocked by war
- after having enough cash (i had ~100mio. Second had ~5mio) start accepting every bank loan
- Start a strategic warfare
-- Look for the biggest countries and take them
-- make best relations with them (Take 5-10)
-- Start a war every 11 rounds (on best relations. otherwise more turns are needed) and take over all other countries
--- at this point you can start letting properties in core regions stay (any not border region)
- start politics and block your oppenents from doing anything while cutting their property in half (the last two political options)
It took me ~400 rounds while i just skipped the last ~150 rounds and started only a war every 11 rounds. Of course i still checked every turn for new contracts.
I didn't found a relation between using my guards and bancrupting some banks even after investing ~3mio fear in one turn on my last oppenent...
After round 300 take the 51% IWF (or let someone else take it) game can't be won after round 300 but the auction will be canceled in the future, so you can skip turns faster.
Hope this helps a bit, since i found not a single proper how-to-guide for this killer achievement...