If you read secular history, more than half the Jews who died during the Revolt were killed by other Jews before the Romans started killing any Jews.
The Jews were killing each other, in what could be described as a civil war.
The city split into three sections.
(Rev 16:19) And the great city was divided into three parts,...
Now, let's look at how Josephus described Jerusalem shortly before 70AD:
"it so happened that the sedition at JERUSALEM was revived, and PARTED INTO THREE FACTIONS, and that one faction fought against the other; which partition in such evil cases may be said to be a good thing, and the EFFECT OF DIVINE JUSTICE.” - Josephus, Book V, Chapter 1, Section 1
Do you see how Josephus confirms the fulfillment of Rev 16:19?