Thanks to the efforts of The Legion of Doom, The Still Force is strengthened, which halts the expansion of the universe and weakens the cosmic membrane holding Umbrax in check. This further allows Sinestro, who found a way to harness the power of the Invisible Emotional Spectrum without being taken over by it, to assert his will over The Earth and the planets already under Umbrax’s control. He then starts recruiting all the people of Earth who are ruled by self-loathing as foot-soldiers for his Ultraviolet Lantern Corps.
Precisely why Sinestro needs an army of mindless thralls with a power exceeding that of the Green Lantern Corps is unclear. Doubtlessly this is all a part of Lex Luthor’s master plan to save the multiverse but it’s unlikely the Justice League will approve of the apparently reformed Luthor’s actions. Of course with the power Luthor and The Legion of Doom now command, it seems there is little The League can do to thwart their designs.