There are several reasons why Jesus could not return before the 21st century, but the one I would like to point out now has to due with the 200 million unit army in Revelation 9. In 1830 the population was 1 billion for the first time. In 1930 it was 2 billion. Certainly not 1 in 10 people would congregate in the middle east over war.

As of last year it reached 7 billion.

200 million / 7 billion = 1 in 35 people. That's possible.

"And the number of the army of the horsemen were two hundred thousand thousand: and I heard the number of them" (Rev. 9.16).

Perhaps it doesn't have to be fully 200 million souls, but at least 200 million military pieces including drones.

Did you know that all the horizontal drilling and fracking for Shale Oil in United States is enough to last only a few years. If there are only 500 billion barrels world wide of this unconventional stuff / 100 billion consumed per year = supply for 5 more years. Big deal!

So we can maintain our addiction to oil for another 5 years before prices get real hefty and thus, the need to battle over oil in the middle east.