Here's another fanfic based on the Worldwar series: Worldwar: Discovering the Balance. This takes in the Stargate Universe in which the Race were 60 years late in arriving to Earth, but the invasion is fortunately averted as SG-1 with Asgard-based spaceships engaged Atvar at gunship diplomacy. In which SG-1 negotiated for the Race to leave Earth alone and settle another desert-like planet discovered by Stargate Command or their home planet is nuked with energy weapons from orbit.
I really love the scenario of the story as to what if the Race had to deal with modern day Earth, in this case the Stargate Earth. Instead of outright destroying the Race, Earth's various governments decide not to and be simply "neighbors" with the Race, and a length of time in convincing the stubborn Lizards to realize that the universe is much bigger than they can possibly imagined. It pretty much captures the Race characters' mentality and their reactions to Earth's advancement, and their difficult grasp of the fact that they are not the one in the center of the universe.
Although, the crossover is not only between Stargate and Worldwar, but also the remake Battlestar Galactica based on another fanfic, Reunions Are A Bitch. In the latter, the Twelve Colonies made a preemptive attack on the Cylons after discovering the machines' machination for the destruction of the colonies, and discovered Earth and declared a crusade on the planet for "straying away" from their polytheistic-based society. Although the 12 Colonies' battlestars are ultimately outgunned by Asgard technology.
The story continues in Worldwar: The Balance Destroyed, where the 12 Colonies discovered the Race's existence and decide to invade Home.