The "End" here is encompassing different things from Mat 24
vv 4-14 is the initial sorrows and the reports of wars and trials and tribulations marking the biggining of the "end times" for all generations
vv 15-28 begins talking about the "Great Tribulation". Here, it is understood the great tribulation is the entire period that Christians have been pursecuted against. It is the Tribulation throughout history beginning from 33 AD until present. We are in the Great Tribulation today.
vv 29-31 is talking about the return of the Son of Man. The "end" of the age.
Many theologians have tried to disect these apocalyptic passages and place them in a chronological sequence but I think Jesus deliberately moves in and out of context and events in order to convey the idea that we are not to make predictions. However to hopefully help you understand this passage as it has helped me I find vv 13 to mean several things.
The "End" can be referring to the destruction of the temple of Jerusalem. See disciples first question based on vv 1-2
The "End" can be also referring to the end of the age or as JW's say "the conclusion of the system of things", or when Jesus actually returns. The second advent.
The "End" can also refer to the end of ones life. Christians must endure the tribulations placed on them by the Devil and resist their Earthly passions and carry their cross or as JW's say "torture stake" and actuate and manifest their salvation until physical death.
In vv 34 Jesus uses the word "generation". This refers to the generation of Christians from Pentecost 33 AD until present day.
Remember that the Apostle Paul saw "the end" in a sense as well as we do today. We are all part of that "generation". When we die we inherit a fortaste of that Kingdom awaiting the final fullfillment when our bodies are resurrected like the apostle paul is also awaiting the resurrection. Therefore it does not matter what time period a Christian lives in. There is no advantage to living now than say in the first century. The only "end" thing left is the coming of the Messiah and it is not yet. The "spiritual" battle between the antichrist and Jesus or Armageddon is also still future. But it is not a physical battle.
Remember also that based on other Bible scriptures we see that the Kingdom of God is allready present in a partial fullfillment. We experience the Kingdom of God in the Church, and in our hearts, and when we die we are brought into a foretaste of the Kingdom waiting for the final fullfillment. Rev 6:9-11
Hope this helps a bit