The Thanagarian invasion was a major event that sparked the expansion of the Justice League.
Thanagarians came to Earth posing as mankind's only hope against the Gordanians who were on their way to Earth in order to enslave it under their rule. Under this guise, the Thangarians planned to use a device that would both destroy the Earth and give the Thangarians access to the Gordanians homeworld, allowing them to once and for all destroy the Gordanians. Vigilante was among what was more than likely many superheroes to be taken prisoner during this invasion. After Batman found out their real plans, Hro Talak, the Thangarian commander, was forced to put the Earth and its defenses and communications offline while they built the supposed shield to protect the Earth. The invading forces also declared martial law and deprived people of their legal rights. Only when Batman crashed the Watchtower into their "little science project" was the device destroyed, crushing the Thangarians' hopes of bypassing the Gordanians.
Despite her redemptive turn to halt the invasion, Shayera Hol was still the subject of widespread criticism for her role as a Thanagarian spy betraying everyone she trusted. The Flash, meanwhile, was honored for his resistance and defense of the Earth.