Q. What is it that brings all nations together against Jerusalem? What is the common cause that unites the entire world against it? Do they not know, or not believe, that they have declared war on Almighty God Himself?
A. Good question. The simple answer is that Jerusalem is the only place on Earth God has reserved for Himself (2 Chron. 6:6). Satan wants the Earth all to himself and can’t share it with anyone, especially not with God. This is demonstrated by his claim in Isaiah 14: 14 that he’ll make himself “like the Most High”. According to Genesis 14:19 the particular Hebrew phrase Isaiah used means “Possessor of Heaven and Earth”. As long as God lays claim to even part of Earth, Satan can’t make good on his boast.
At the End of the Age non-believers on Earth will be persuaded that Satan is the good guy, and God is the enemy. This is the great lie Paul spoke of in 2 Thes.2:9-12. They’ll believe they’re doing the right thing by siding with Satan, and that “the power of right” will make them victorious. In the meantime, I believe Satan has put it into the minds of rebellious men to desire Jerusalem in preparation for this great confrontation.