The land of Metavira needs your help! Contract additional mercenaries as you explore, capture, and hold new territory so the natives can harvest the valuable trees from which a revolutionary medicine can be extracted. The more trees you hold, the more money you make. The more money you have, the more you can do, such as hire native guards, hire more mercs, in order to take the offense and clear the sector of enemies. You will also need to retrieve certain objects from behind enemy lines, rescue captured personnel, capture equipment, and more. Hire a good mechanic in order to get your equipment and guns repaired, and to "enhance" them with various add-ons. Travel through lush jungles, treacherous rivers (with venomous snakes!), and more as you seek to free Metavira. Eventually, you'll meet up with the bad guys' leader in his compound for the final showdown...
Jagged Alliance is a turn-based tactical combat game with a mixture of strategy, reminiscent of X-Com games. On the "strategic view", you get to see the various sectors of Metavira. You start with just one sector, with a few trees for your income. You need to hold more sectors in order to increase the number of trees you hold, which will increase your income. You can hire/fire mercs.
Each merc can move or shoot or perform any of the other actions as long as they sitll have action points. Each of the mercenaries have personality. Some work well with others, others won't. You'll need shooters (both long and short guns), explosive experts (to set/disarm bombs/traps), mechanics/gunsmiths (fix/modify your equipment), doctors/nurses (to heal wounded mercs). Each merc has a different price, so you'll need to balance what you can afford vs. what you need. Manage the equipment as well.
If you move into an enemy-held sector, the game moves to combat mode, where you get an over-head slightly-isometric turn-based tactical combat that's based on "action points", which limits the amount of action each merc can perform. You can do this, or that, but not both. The action continues until the sector is no longer contested (either one side got wiped out, or retreated to another sector, or both).
After the sector is clear, you can call in native guards to "hold" the sector (you need to pay for them as well) as well as hire more natives to process the "new" trees. You will also need to get the mercs to the homebase if any one was wounded, and let the doctor/nurse treat them. Idle mercs at the base can train to improve their ratings. Some scripted events and some random events will keep you busy such as poisoned water, a virus that attacks the trees, kidnapped daughter of chief, and others.
So to summarize, you need to manage the mercs (and their salary), their equipment (who gets what), arrange for backup (mercs at base) and medical treatment (doctor/nurse) while taking into account their personalities and strengths. You also need to manage the strategic aspects as you need to "conquer" each sector and then send enough guards to hold the sector after you retrieve the mercs. You manage the money as you need to balance the expenditures (mercs, equipment, guards, natives, etc.) against the income (the trees). You also get to manage the tactical aspects of the battle as you decide each move and shot. A full complement of mercenary supplies (from revolvers to M-16s, plus bombs, grenades, mines, flak jackets, helmets, and more) are available.