Just to toss in, another thought might be to start a war - the PCs are essentially a special ops team. The y don't have to make big decisions about where to go, they're sent on missions with fairly specific goals - destroy object/person x; bring back object/person x; see what's at location y and report back; deliver person/object x to this place, or to that person; hold location x until relieved.
The emphasis for them remains on tactics and fighting, but there's a broader purpose behind it besides more lewts, and there are roleplaying opportunities you can put in that are quite reasonable: dealing with local refugess, spy contacts, potential traitors, prisoners, persuading local villagers to not report your presence, and so forth.
For the GM, you can use the decisions of the players, and how they handle situations both combat and noncombat to infuence the overall events of the war. If you're at all into that kind of thing, it can provide some interest for you, and the players can dig into overall strategy and wider events of they want to, or pretty much ignore them if they just want to follow directions and blow stuff up. And the history of warfare can provide inspiration for all kinds of situations, terrain, and opponents.