Historicism is a method of interpretation in Christian eschatology that associates biblical prophecies with actual historical events (which may also be symbolic of repeated occurrences). This means that many things in Revelation have occurred while other things have not. Also that the symbols in the visions match major historical events in remarkable ways and in a chronology that actually occurs in the annals of history.
Historical interpretation naturally takes much more work than pure symbolic or mere speculative interpretation because one actually has to be familiar with the history of the world as it pertains to the Christian church. To be expected, the outcome of such hard work also leads to large amounts of information to provide as there is so much evidence to weigh. For example, this old classic on Revelation (Horae Apocalypticae; or, A commentary on the Apocalypse, critical and historical; including also an examination of the chief prophecies of Daniel 1862) is around 3000 pages of detailed arguments wrapping history around Revelation in chronological order.