The Doctrine and Covenants, Section 63:32-33

32 I, the Lord, am angry with the wicked; I am holding my Spirit from the inhabitants of the earth.

33 I have sworn in my wrath, and decreed wars upon the face of the earth, and the wicked shall slay the wicked, and fear shall come upon every man;

History of the Church, Joseph Smith 6:58

I prophesy, in the name of the Lord God of Israel, anguish and wrath and tribulation and the withdrawing of the Spirit of God from the earth await this generation, until they are visited with utter desolation. This generation is as corrupt as the generation of the Jews that crucified Christ; and if He were here to-day, and should preach the same doctrine He did then, they would put Him to death. I defy all the world to destroy the work of God; and I prophesy they never will have power to kill me till my work is accomplished, and I am ready to die.

Journal of Discourses, Orson Pratt 20:18

[W]ithout the Spirit of God upon them, when they have not that spirit of humanity that now characterizes many of the wars amongst the nations, when they are left to themselves, there will be no quarter given, no prisoners taken, but a war of destruction, of desolation, of the burning of the cities and villages, until the land is laid desolate.

Journal of Discourses, Orson Pratt 7:29

By-and-by, when the Lord has made bare his arm in signs, in great wonders, and in mighty deeds, through the instrumentality of his servants the Seventies, and through the instrumentality of the churches that shall be built up, and the nations and kingdoms of the earth have been faithfully and fully warned, and the Lord has fulfilled and accomplished all things that have been written in the Book of Mormon, and in other revelations pertaining to the preaching of the Gospel to the nations of the Gentiles and to the nations of Israel, by-and-by the Spirit of God will entirely withdraw from those Gentile nations, and leave them to themselves. Then they will find something else to do besides warring against the Saints in their midst–besides raising their sword and fighting against the Lamb of God; for then war will commence in earnest, and such a war as probably never entered into the hearts of men in our age to conceive of. No nation of the Gentiles upon the face of the whole earth but what will be engaged in deadly war, except the Latter-day Kingdom.