In Muslim End-Time ahadith, Ya'juj and Ma'juj (Gog and Magog) will wreak havoc over the globe prior to the arrival of the Mahdi who kills the Dajjal and establishes a global government of shari'a law.
According to some imams, "Dajjal" ("the deceiver") is a descriptive title, while Ya'juj and Ma'juj are two actual names for the Dajjal. They say that Ya'juj / Gog was the ancient chief of the Russian tribes, and that Ma'juj was the ancient chief of the Teutonic tribes. Ergo, "Ya'juj and Ma'juj oppressing the earth and ravaging its resources" was Mohammed's allegorical way of prophesying that the two Western evils of atheistic Communism and materialistic Capitalism would overrun the globe in the 20th century, persecuting mankind and raping / polluting the environment.
In the imam's telling of things, the Taliban (not Reagan & Thatcher) brought down the Soviet Union (Ya'juj / Gog).
So the only facet of the Dajjal left to be destroyed by the Mahdi is Western Capitalism (Ma'juj / Magog -- the US and EU, mainly). Then Islamic economics under shari'a can "liberate" mankind.
It must be understood that from their point of view, the global jihad is a "human rights movement" (see Sayid Qutb's Milestones).
For more information on Muslim End-Time beliefs, see my FR Homepage and Links page.
Thank you Dajjal for posting the additional background info.