JMich: Jagged Alliance was the first one, where you had to free the island of Metavira (if I recall correctly)
Jagged Alliance: Deadly Games was the second one, which was mostly scenario based, aka not as open as JA1. You could think of it as a stand alone expansion, using the same (mostly) characters as JA1, but with a different goal.
Jagged Alliance 2 was the third game published, which is set a few years after the Metavira one. You will meet many (if not all) characters from the first game, along with a lot of new ones. You can play the second without playing the first one, but think of it like watching Lethal Weapon 2 without first watching Lethal Weapon 1. You can get the plot, you can enjoy the game, but you may miss a few jokes about the previous one.
Jagged Alliance 2: Unfinished Business is the fourth one, which takes place some time after the events of JA2. This is mostly a combat oriented game, which has almost no economic factors in it. It truly is a "Change sector, Clear Sector, Repeat". It did introduce some more guns, and a few more mercenaries, but no idea whether you'd like it or not. On the other hand, it included a campaign editor, which allowed users to make their own mods to use with JA2:UB.
Finally, Jagged Alliance 2: Wildfire is the 5th game published, which is a remake of JA2. There were quite a few improvements, including (but not limited) to increased squad size, higher resolution support, improved maps and higher difficulty. The game also included JA2's source code on the cd it came on, but not JA2:WF source code.
All of the JA2 games can be played on their own, without the need to install JA2 first. However, my suggestion would be getting JA2, especially due to the 1.13 patch.
Hope this helps clarify the situation a bit, even if I may have made a few mistakes about the games.
Thanks for the info, I have ja2 bought here but havent installed 1.13 yet because another tread here said that it was better to play the 1.12 first and then 1.13 to notice the diffrence betwean 2 patches.
