After Nero heard about the failure of Cestius Gallus to crush the Jewish rebellion, he dispatched his most able general Vespasian to do it right this time. Over the winter of 66-67, Vespasian and Titus assembled three legions and hordes of other auxiliaries and mercenaries to launch the attack in the Spring of AD 67.
Vespasian was successful in destroying all the fortresses of all areas outside of Jerusalem (except for Herodium, Machaerus, and Masada). When he was ready to begin the assault on Jerusalem, he received the news that Nero died. The war effort was put on hold until affairs in Rome could be restabilized.
Past fulfillment
A look at the topography will reveal that Armageddon is a small rise among others on a small elevated plateau close to a large level coastal plain large enough to accommodate many thousands of troops. Being that it doesn't dominate the surrounding area, it is not an obvious target, yet it is useful as a garrison and it has a water source. This explains why Josiah used the terrain to mask his approach as he attempted to ambush the Egyptians who were on their way to attack the Chaldeans. The reason was he was allied with the Chaldeans and he had the obligation to attack them. Within only a few years, other Jewish kings would revolt with the promised support of the Egyptians, yet they were unsuccessful and Jerusalem would be destroyed.
As a historical matter, gatherings by enemies such as the Assyrians, Chaldeans and later the Romans occurred at Megiddo as a staging ground or assembly area for subsequent deployments toward the fortified garrisons uphill from the coast.
This is consistent with the preterist interpretation that the seventh bowl of wrath refers to events culminating in the destruction of Jerusalem in 70 AD. However, one indication that the book predicts a future event is the mention of an army from the east of 200 million, a number that would not have been possible in any battle of that period.(Totally symbolic number)
https://www.dummies.com/education/history/world-history/armageddon-and-the-book-of-revelation/