It's commonly assumed that democracy won't work for wars, especially long wars. It's just not true that it won't work.
kb2tvl's comments bear this view, and he has one excellent point. Having all eight luxuries and many marketplaces is probably the best thing you can do. Trade for them if needed (obviously) Suffrage is nice, but not required. Police statsions help. The last thing I want to do however is a defensive war in democracy.
The key, frankly, is in not losing many units, and not having your cities attacked. If you let the AI come to you and attack your cities your weariness will skyrocket. ONE way to do well is to have a massive force and just roll over your foe(s). But I use two other tactics to have an extreme warmonger game and stay in democracy.
- First, I take it to their territory and use combined arms, including strong defenders and heavy bombardment to cut losses, and fast units to actually attack the cities. Their retreat ability, and ability to raze a city then step back and get defended helps alot.
- Oscillating war. Your war weariness levels are calculated on a per-civ basis, then added up. If you switch between opponents, hitting hard, taking concessions, and move on to another foe, serious war weariness seldomly settles in.
- Your income (if you have 8 lux) will quite likely be stronger in democracy at 40% lux rate, than in monarchy at 0%. When it gets to 50% it starts to even out or turn slightly to favoring Monarchy. If I'm going to stop soon, I use several entertainers where needed and keep in Democracy.
- In a recent deity game where I did choose an attack style with combined arms, had 8 lux and all happiness buildings, I entered democracy and proceeding to conquest, wiping out 4-5 civs, but oscillating. It wasn't until the very last foe, the world superpower, where my losses were high enough that democracy was about to fail. I switched to... Republic!! That let me go from 50(almost 60%) lux and an untenable deficit to 40% lux slider, where I stayed the rest of the game.
If your style is to conquer by throwing heavy numbers of units at foes and take a fair amount of losses along the way, democracy won't work for extended periods. Then again, you'll probably be fine switching to Monarchy and might finish the game early than a slower approach -- it's a question of what style you like.
pterrok's comments above are also very good.
Charis