In one word: Oil
Read Daniel 11:24, a passage speaking on the future antichrist:
"He shall enter peaceably, even into the richest (or fattest) places of the province; and he shall do what his fathers have not done, nor his forefathers: he shall disperse among them the plunder, spoil, and riches; and he shall devise his plans against the strongholds, but only for a time."
- The word Richest or Fattest comes from the root of the word Oil.
- The word Province translates as the word Medina.
The Antichrist will be controlling the oil. Therefore, for some reason or another, the Kings of the East will be forced to march toward the middle east--they need the oil! As they march, they will cross the Euphrates river which scriptures states will dry up in the latter days, and then eventually meet up to fight against the Antichrist's army in the Valley of Megiddo.
So why the battle of Armageddon? The battle--a necessary fight to secure most important resource on earth that is in short supply and tightly controlled by the world leader. Thus, the Kings of the East march their million man army west eventually meeting near the Antichrist's headquarters, Jerusalem.
Author and Preacher Perry Stone presents a great video on the topic: Armageddon Video
The part on Megiddo and the Battle of Armageddon is near the half way mark.