Valley of Megiddo - Jezreel
Megiddo (which is within the valley of Jezreel) is a city located in the territory given to the Israelite tribe of Manasseh when they entered the promised land. The word itself is translated from the Hebrew gadad (Strong's Concordance number #H1413), meaning to slaughter or cut off. Before Joshua led the children of Israel into the land, it was a Canaanite royal city (Joshua 12:21). It took the Israelites quite a bit of time to finally overtake and possess the city.
Sometime after the city came under the control of Israel it was restored and greatly fortified under the reign of King Solomon, "And this is the reason for the labor force which King Solomon raised: to build the house of the Lord, his own house, the Millo, the wall of Jerusalem, Hazor, Megiddo, and Gezer" (1Kings 9:15)
Excavations have unearthed 26 layers of ruins, indicating a long period of settlement in the area. Anciently, it was important because it guarded the western branch of a narrow pass and trade route connecting Egypt and Assyria. The plain of Megiddo is part of the plain of Esdraelon (Jezreel valley), which is known as the great battlefield of Palestine. Many decisive battles, especially in ancient times, have been fought in or near this area.
The word Armageddon, which occurs only once in the Bible, is a combination of two Hebrew words. The first word is har, which means mountain or a range of hills, and mgiddown, which is called 'Megiddo' in English.
Armageddon is frequently used as a term to label the entire time period starting from when the armies of the world begin to gather together (along with the beast and false prophet) to FIGHT Jesus to his actual return and victorious war over the forces of evil. It is after this victory that Christ sets up His Millennial Kingdom on the earth.
In the sixteenth chapter of Revelation the word Armageddon is used to designate the actual location of the last world war, which is within the valley of Jezreel - Megiddo.