Bible prophecies need to be read in the context of the times in which they were written. They generally take the form of warnings of catastrophe if the people to whom they are addressed don't change their ways - usually adopting the religion or culture of people they live among or neighbour.
One way of claiming that a prophecy has been fulfilled is to pick on an event or set of events and read it or them back into ancient scripture, and twist that scripture to make it fit the events and mean something the original prophet or scribe could not have meant or conceptualise.
Another is to accredit an ancient prophet with prophesying events that he could never have known about - if indeed he was real, and not a legend or a demi-god adopted by the Israelites but transformed to be consistent with their later monotheistic beliefs. This has happened in the gospels, which are littered with claims that something was done to fulfil a prophecy.
And theologians often read back later scriptures, reflecting beliefs current at the time they were written, to earlier scriptures. For example, John identifies the great dragon in Revelation, that ancient serpent (from Sumerian myth, symbolising the waters of chaos), with Satan and the Greek equivalent the Devil (from Diabolos that has similar meanings as Satan, such as Accuser); that has been read back into Genesis 3 to claim that the serpent in the garden of Eden was Satan - even though these were separate myths.
As another example, the prophecies in Revelation were expected to happen within the lifetimes of those living at the time, the 1st or 2nd century CE, followed by 1,000 years. They just didn't happen, although believers push them further and further into the future to other times, when they continue not to happen.