I disliked this game before I understood it, but it's fun once you get it.
Mainly, you have to consider morale, which is equally valuable to manpower. It changes when territories are captured or battles are fought, so it introduces momentum, discouraging sacrifices and overextension.
There's also a rule that you can only move 5 units per turn, even if you have more. This incentivizes consolidating your units for efficiency. However, joining two units averages their morale (weighted by manpower) instead of adding it, so you lose some force doing this.
Identifying the best starting position is crucial. It needs to be decisively superior to the nearest neighbor and allow for fast expansion. If you can obtain a majority of cities, you're golden.
I like to play a random map on hard mode and see if I can take over without using the morale-boosting speech. Sometimes I even manage without pacts, but the bots can be tough when they gang up (especially because of the 5-move rule).
The bots are a little dumb and sometimes there are visual glitches with naval units, but generally this game is well-made and enduring in its appeal.